- Describe the different kinds of sleep disorders.
- Describe the causes of different sleep disorders.
- Analyze different treatment options for sleep disorders.
- Describe current research on the connection between sleep disorders and other physical health conditions.
Research has demonstrated that good sleep habits result in improved health and psychological functioning (Hyyppa & Kronholm, 1989). In fact poor sleep quality can result in severe psychiatric symptoms. Worldwide, approximately 30 percent of adults report difficulty initiating or maintaining sleep or experiencing poor sleep quality.
About 50 to 70 million Americans have sleep or wakefulness disorders. Sleep deficiency and untreated sleep disorders are associated with a growing number of health problems, including heart disease, high blood pressure, stroke, diabetes, obesity, and certain cancers. Sleep disorders can also be costly. Each year sleep disorders, sleep deprivation, and sleepiness add to the national health care bill. Undiagnosed sleep apnea alone is estimated to cost the US $150 billion annually. Additional costs to society for related health problems, lost worker productivity, and accidents make sleep disorders a serious public health concern.
In this section insomnia, circadian rhythm disorders, sleep apnea and narcolepsy are discussed.
Insomnia is a common sleep disorder. With insomnia, you may have trouble falling asleep, staying asleep, or getting good quality sleep. Chronic (long-term) insomnia occurs three or more nights a week, lasts more than three months, and cannot be fully explained by another health problem or a medicine.
Insomnia can affect your memory and concentration. Chronic insomnia raises your risk of high blood pressure, coronary heart disease, diabetes, and cancer.
In addition to finding out your medical history and having you keep a sleep diary, your doctor may have you take the following tests.
- A sleep study to look for other sleep problems, such as circadian rhythm disorders, sleep apnea, and narcolepsy.
- Actigraphy to measure how well you sleep. This requires you wear a small motion sensor three to 14 days.
- Blood tests to check for thyroid problems or other medical conditions that can affect sleep.
In the short term, insomnia can make it hard to concentrate or think clearly. You may feel irritable, sad, and unrested or have headaches. Insomnia raises your risk of falling, having a road accident, or missing work.
In addition, chronic insomnia can affect how well your brain, heart, and other parts of your body work. It can raise your risk of certain health problems or make existing problems worse. These conditions include:
- Breathing problems such as asthma
- Heart problems such as arrhythmia, heart failure, coronary heart disease, and high blood pressure
- Mental health conditions such as anxiety, depression, and thoughts of suicide. Insomnia can also make it difficult for you to stick to treatment for a substance use disorder.
- Pain. People who have chronic pain and insomnia may become more aware of and distressed by their pain.
- Pregnancy complications such as having more pain during labor, giving birth preterm, needing a cesarean section (C-section), and having a baby with low birth weight.
- Problems with your immune system, your body’s natural defense against germs and sickness. These problems can lead to in your body or make it harder to fight infections.
- Problems with your . Not getting enough sleep can change the levels of hormones that control hunger and how you break down food. This can raise the risk of overweight and obesity, metabolic syndrome, and diabetes.
Doctors may recommend healthy lifestyle habits such as a regular sleep schedule, cognitive behavioral therapy for insomnia, and medicines to help manage the insomnia.
Many prescription medicines are used to treat insomnia. Some are meant for short-term use while others are meant for longer-term use. Some insomnia medicines can be habit-forming and all of these medicines may cause dizziness, drowsiness, or worsening of depression or suicidal thoughts. All of the medicines listed below may also cause insomnia.
- Benzodiazepines, like Valium, and Benzodiazepine receptors agonists, such as zolpidem, zaleplon, and eszopiclone can be habit-forming and should be taken for only a few weeks. Benzodiazepines are GABA agonists. Remember, from chapter *, that GABA is one of the most common inhibitory neurotransmitters in the central nervous system. Hence Benzodiazepines (and Benzodiazepine receptor agonists) make it even less likely that neurons will fire. Additional side effects of Benzodiazepine receptor agonists may include anxiety. Rare side effects may include a severe allergic reaction or unintentionally doing activities while asleep such as walking, eating, or driving.
- Melatonin receptor agonists, such as ramelteon. Rare side effects may include doing activities while asleep such as walking, eating or driving or a severe allergic reaction.
- Orexin receptor antagonists, such as suvorexant. This medicine is not recommended for people who have narcolepsy. Rare side effects may include doing activities while asleep such as walking, eating, or driving or not being able to move or speak for several minutes while going to sleep or waking up.
In some special cases healthcare providers may prescribe medicines that are commonly used for other health conditions but are not yet approved by the FDA to treat insomnia. Some of these medicines may include antidepressants, antipsychotics, and anticonvulsants.
Over-the-counter medicines and supplements
Some over-the-counter (OTC) products that contain antihistamines are sold as sleep aids. Although these products might make you sleepy, talk to your doctor before taking them. Antihistamines can be unsafe for some people. Also, these products may not be the best treatment for your insomnia. Your doctor can advise you whether these products will help you.
Melatonin supplements are lab-made versions of the sleep hormone . Many people take melatonin supplements to improve their sleep. However, research has not proven that melatonin is an effective treatment for insomnia. Talk to your doctor before using these supplements. Dietary supplements can be beneficial to your health, but they can also have health risks.
The U.S. Food and Drug Administration regulates dietary supplements under a different set of regulations than those covering "conventional" foods and medicines. It does not have the authority to review dietary supplement products for safety and effectiveness before they are marketed.
Side effects of melatonin may include daytime sleepiness, headaches, upset stomach, and worsening depression. It can also affect your body's control of blood pressure, causing high or low blood pressure.
Your doctor may recommend that you use light therapy to set and maintain your sleep-wake cycle. With this treatment, you plan time each day to sit in front of a light box, which produces bright light similar to sunlight.
Sleep apnea is a common condition in the United States. It can occur when the upper airway becomes blocked repeatedly during sleep, reducing or completely stopping airflow. This is known as obstructive sleep apnea. If the brain does not send the signals needed to breathe, the condition may be called central sleep apnea.
Healthcare providers use sleep studies to diagnose sleep apnea. They record the number of episodes of slow or stopped breathing and the number of central sleep apnea events detected in an hour. They also determine whether oxygen levels in the blood are lower during these events.
Sleep studies can be done in a special center or at home. Studies at a sleep center can detect apnea events, detect low or high levels of activity in muscles that control breathing, monitor blood oxygen levels, brain and heart activity during sleep.
Other medical conditions that can cause sleep apnea are diagnosed in the following manner:
- Blood tests to check the levels of certain hormones and to rule out endocrine disorders that could be contributing to sleep apnea. Thyroid hormone can rule out hypothyroidism. Growth hormone tests can rule out acromegaly. Total testosterone and dehydroepiandrosterone sulphate (DHEAS) tests can help rule out polycystic ovary syndrome (PCOS).
- Pelvic ultrasound to examine the ovaries and detect cysts. This can rule out PCOS.
Doctors may want to know whether there is use of medicines, such as opioids, that could be affecting sleep or causing breathing symptoms of sleep apnea. Doctors may also want to know whether the patient has traveled recently to altitudes greater than 6,000 feet, because these low-oxygen environments can cause symptoms of sleep apnea for a few weeks after traveling.
Undiagnosed or untreated sleep apnea can lead to serious complications such as heart attack, glaucoma, diabetes, cancer, and cognitive and behavioral disorders.
Breathing devices such as continuous positive air pressure (CPAP) machines and lifestyle changes are common sleep apnea treatments.
Narcolepsy is a chronic neurological disorder that affects the brain’s ability to control sleep-wake cycles. People with narcolepsy may feel rested after waking, but then feel very sleepy throughout much of the day. Many individuals with narcolepsy also experience uneven and interrupted sleep that can involve waking up frequently during the night.
Narcolepsy is a lifelong problem, but it does not usually worsen as the person ages. Symptoms can partially improve over time, but they will never disappear completely. The most typical symptoms are excessive daytime sleepiness, cataplexy, sleep paralysis, and hallucinations. Though all have excessive daytime sleepiness, only 10 to 25 percent of affected individuals will experience all of the other symptoms during the course of their illness.
- Excessive daytime sleepiness (EDS). All individuals with narcolepsy have EDS, and it is often the most obvious symptom. EDS is characterized by persistent sleepiness, regardless of how much sleep an individual gets at night. However, sleepiness in narcolepsy is more like a “sleep attack”, where an overwhelming sense of sleepiness comes on quickly.
- Cataplexy. This sudden loss of muscle tone while a person is awake leads to weakness and a loss of voluntary muscle control. It is often triggered by sudden, strong emotions such as laughter, fear, anger, stress, or excitement. Some people may only have one or two attacks in a lifetime, while others may experience many attacks a day. Attacks may be mild and involve only a momentary sense of minor weakness in a limited number of muscles, such as a slight drooping of the eyelids. The most severe attacks result in a total body collapse during which individuals are unable to move, speak, or keep their eyes open. But even during the most severe episodes, people remain fully conscious, a characteristic that distinguishes cataplexy from fainting or seizure disorders. The loss of muscle tone during cataplexy resembles paralysis of muscle activity that naturally occurs during REM sleep.
- Sleep paralysis. The temporary inability to move or speak while falling asleep or waking up usually lasts only a few seconds or minutes and is similar to REM-induced inhibitions of voluntary muscle activity. Sleep paralysis resembles cataplexy except it occurs at the edges of sleep.
- Hallucinations. Very vivid and sometimes frightening images can accompany sleep paralysis and usually occur when people are falling asleep or waking up. Most often the content is primarily visual, but any of the other senses can be involved.
Additional symptoms of narcolepsy include:
- Fragmented sleep and insomnia. While individuals with narcolepsy are very sleepy during the day, they usually also experience difficulties staying asleep at night. Sleep may be disrupted by insomnia, vivid dreaming, sleep apnea, acting out while dreaming, and periodic leg movements.
- Automatic behaviors. Individuals with narcolepsy may experience temporary sleep episodes that can be very brief, lasting no more than seconds at a time. A person falls asleep during an activity (e.g., eating, talking) and automatically continues the activity for a few seconds or minutes without conscious awareness of what they are doing. This happens most often while people are engaged in habitual activities such as typing or driving. They cannot recall their actions, and their performance is almost always impaired.
In a normal sleep cycle, a person enters rapid eye movement (REM) sleep after about 60 to 90 minutes. Dreams occur during REM sleep, and the brain keeps muscles limp during this sleep stage, which prevents people from acting out their dreams. People with narcolepsy frequently enter REM sleep rapidly, within 15 minutes of falling asleep. Also, the muscle weakness or dream activity of REM sleep can occur during wakefulness or be absent during sleep. This helps explain some symptoms of narcolepsy. Narcolepsy affects both males and females equally. Symptoms often start in childhood, adolescence, or young adulthood (ages 7 to 25), but can occur at any time in life. It is estimated that anywhere from 135,000 to 200,000 people in the United States have narcolepsy. However, since this condition often goes undiagnosed, the number may be higher. Since people with narcolepsy are often misdiagnosed with other conditions, such as psychiatric disorders or emotional problems, it can take years for someone to get the proper diagnosis.
Individuals may be asked by their doctor to keep a sleep journal noting the times of sleep and symptoms over a one- to two-week period. Although none of the major symptoms are exclusive to narcolepsy, cataplexy is the most specific symptom and occurs in almost no other diseases.
A physical exam can rule out or identify other neurological conditions that may be causing the symptoms. Two specialized tests, which can be performed in a sleep disorders clinic, are required to establish a diagnosis of narcolepsy:
- Polysomnogram (PSG or sleep study). The PSG is an overnight recording of brain and muscle activity, breathing, and eye movements. A PSG can help reveal whether REM sleep occurs early in the sleep cycle and if an individual's symptoms result from another condition such as sleep apnea.
- Multiple sleep latency test (MSLT). The MSLT assesses daytime sleepiness by measuring how quickly a person falls asleep and whether they enter REM sleep. On the day after the PSG, an individual is asked to take five short naps separated by two hours over the course of a day. If an individual falls asleep in less than 8 minutes on average over the five naps, this indicates excessive daytime sleepiness. However, individuals with narcolepsy also have REM sleep start abnormally quickly. If REM sleep happens within 15 minutes at least two times out of the five naps and the sleep study the night before, this is likely an abnormality caused by narcolepsy.
Occasionally, it may be helpful to measure the level of hypocretin in the fluid that surrounds the brain and spinal cord. To perform this test, a doctor will withdraw a sample of the cerebrospinal fluid using a lumbar puncture (also called a spinal tap) and measure the level of hypocretin-1. In the absence of other serious medical conditions, low hypocretin-1 levels almost certainly indicate type 1 narcolepsy.
Narcolepsy may have several causes. Nearly all people with narcolepsy who have cataplexy have extremely low levels of the naturally occurring chemical hypocretin, which promotes wakefulness and regulates REM sleep. Hypocretin levels are usually normal in people who have narcolepsy without cataplexy.
Although the cause of narcolepsy is not completely understood, current research suggests that narcolepsy may be the result of a combination of factors working together to cause a lack of hypocretin. These factors include:
- Autoimmune disorders. When cataplexy is present, the cause is most often the loss of brain cells that produce hypocretin. Although the reason for this cell loss is unknown, it appears to be linked to abnormalities in the immune system.
- Family history. Up to 10 percent of individuals diagnosed with narcolepsy with cataplexy report having a close relative with similar symptoms.
- Brain injuries. Rarely, narcolepsy results from traumatic injury to parts of the brain that regulate wakefulness and REM sleep or from tumors and other diseases in the same regions.
Early recognition and diagnosis of narcolepsy could be significant for certain treatment possibilities. Although under debate, autoimmunity is believed to be responsible for the hypocretin neuron loss. Some case reports and uncontrolled small studies suggest that immunomodulatory treatment, such as intravenous immunoglobulin, is able to ameliorate narcolepsy symptoms and influence hypocretin status (see Giannoccaro, 2020 for an overview). Based on the assumption that immunomodulatory treatment could prevent neuronal death, it should be administered as close to disease onset as possible. However, the presence of cataplexy already indicates the loss of the majority of hypocretinergic cells. Recognition of narcolepsy even before cataplexy onset is therefore crucial in order to modify the course of the pathological process. The emerging evidence of T-cell activation in the blood and CSF of narcolepsy type 1 patients in a very early stage of the disease might become useful in early recognition as well as timing of immunomodulatory treatment.
Although there is no cure for narcolepsy, some of the symptoms can be treated with medicines and lifestyle changes. When cataplexy is present, the loss of hypocretin is believed to be irreversible and lifelong. Excessive daytime sleepiness and cataplexy can be controlled in most individuals with medications.
- Modafinil. The initial line of treatment is usually a central nervous system stimulant such as modafinil, which is less addictive and has fewer side effects than older stimulants.
- Amphetamine-like stimulants. In cases where modafinil is not effective, doctors may prescribe amphetamine-like stimulants such as methylphenidate to alleviate EDS. The potential for side effects and abuse is higher so monitoring is necessary.
- Antidepressants. Two classes of antidepressant drugs have proven effective in controlling cataplexy in many individuals: tricyclics (including imipramine, desipramine, clomipramine, and protriptyline) and selective serotonin and noradrenergic reuptake inhibitors (including venlafaxine, fluoxetine, and atomoxetine).
- Sodium oxybate. Sodium oxybate (also known as gamma hydroxybutyrate or GHB) has been approved by the U.S. Food and Drug Administration to treat cataplexy and excessive daytime sleepiness in individuals with narcolepsy.
Not everyone with narcolepsy can consistently maintain a fully normal state of alertness using currently available medications. Drug therapy should accompany various lifestyle changes such as taking short naps, maintaining a regular sleep schedule, avoiding caffeine, large meals and alcohol before bed, avoiding smoking, relaxing before bedtime, and exercising daily. Safety precautions while driving, operating heavy machinery and even walking down long flights of stairs are important.
Circadian Rhythm Disorders (Also known as Sleep-Wake Cycle Disorders)
Circadian rhythm disorders are problems that occur when your sleep-wake cycle is not properly aligned with your environment and interferes with your daily activities.
Your body tries to align your suprachiasmatic nuclei and endogenous sleep-wake cycle to cues from the environment, for example, when it gets light or dark outside, when you eat, and when you are physically active. When your sleep-wake cycle is out of sync with your environment, you may have difficulty sleeping, and the quality of your sleep may be poor. Disruptions of your sleep-wake cycle that interfere with daily activities may mean that you have a circadian rhythm disorder.
Disruptions in your sleep patterns can be temporary and caused by external factors such as your sleep habits, job, or travel. Jet lag and shift work are two major contemporary conditions that are a result of technology and our present social and economic realities. Or a circadian rhythm disorder can be long-term and caused by internal factors such as your age, your genes, or a medical condition. Symptoms may include extreme daytime sleepiness, insomnia, tiredness, decreased alertness, and problems with memory and decision-making.
To diagnose a circadian rhythm disorder, your doctor may ask about your sleep habits, suggest sleep tests, a diary to track when and how long you sleep, and test the levels of certain hormones in your blood or saliva. Your treatment plan will depend on the type and cause of your circadian rhythm disorder. Treatment may include light therapy, medicines to help you fall asleep or stay awake, or healthy lifestyle changes including steps to improve your sleep habits. If left untreated, circadian rhythm disorders may increase the risk of certain health problems or lead to workplace and road accidents.
There are many sleep-wake phase disorders which include Advanced sleep-wake phase disorder, Delayed sleep-wake phase disorder, Irregular sleep-wake rhythm disorder, and Non–24-hour sleep-wake rhythm disorder.
Circadian rhythm disorders cause problems with metabolism in shift workers. When shift work triggers a circadian rhythm disorder, it can disrupt your metabolism in a few ways. Normally, your biological clock helps control your hunger hormones. However, when you do not get enough good-quality sleep, your body makes less leptin, the hormone that tells your body when you are full, and more ghrelin, the hormone that tells your body you are hungry. You may respond by eating larger amounts of food than normal, as well as more fatty, sweet, and salty foods.
Learn about the following ways the NHLBI continues to translate current research into improved health for people who have circadian rhythm disorders. Research on this topic is part of the NHLBI’s broader commitment to advancing sleep science and sleep disorders scientific discovery.
- NHLBI’s National Center on Sleep Disorders Research (NCSDR). For 25 years, the NCSDR has led foundational research on sleep and circadian biology across the NIH and has worked with federal and private organizations to disseminate sleep health information. The NCSDR administers sleep and circadian research projects, training, and educational awareness programs, and serves as an NIH point of contact for federal agencies and public interest organizations. The Center also participates in research translation and dissemination of scientific sleep and circadian advances to healthcare professionals, public health officials, and the public.
- Advancing Circadian Rhythm Research. We have organized workshops to help direct future research into circadian rhythms and circadian rhythm disorders. These workshops have brought together experts in the fields of sleep and circadian rhythm research to identify pertinent areas of research into the role of circadian rhythms in the development and progression of several health conditions. Learn more about Developing Biomarker Arrays Predicting Sleep and Circadian-Coupled Risks to Health and Circadian-Coupled Cellular Function and Disease in Heart, Lung, and Blood.
- Investigating the Link between Circadian Rhythms and Lung Diseases. We have hosted workshops to address current gaps in our understanding of acute and chronic lung diseases. Our workshops have helped direct research to build upon preliminary discoveries showing that lung diseases such as asthma may be influenced by circadian rhythms. Learn more about The Circadian Clock’s Influence on Lung Health.
- Research Conference on Sleep and the Health of Women. This 2018 conference focused on the importance of sleep for women’s health. It showcased a decade of federally funded research advances in understanding the health risks, societal burden, and treatment options associated with sleep deficiency and sleep disorders in women. Topics discussed at this conference included the influence of sleep and circadian rhythms on alcohol consumption and cancer in women, and the social, environmental, and biological factors that affect sleep in women, including during pregnancy, postpartum, and menopause. Learn more from the Research Conference on Sleep and the Health of Women.
- Improving the Quality of Medical School Education on Sleep Disorders. As part of its efforts to ensure that research advances are utilized by healthcare providers, the NCSDR has supported the development of medical school curricula and durable educational materials on sleep disorders, including circadian rhythm disorders.
- Sleep Disorders Research Advisory Board (SDRAB). The NHLBI has administered this specialty program advisory panel since 1993. Board members, including medical professionals, federal partners, and members of the public, meet regularly to provide feedback to the NIH on sleep-related research needs and to discuss how to move sleep research forward. The SDRAB has supported advances to improve our understanding of circadian rhythms and circadian rhythm disorders. Visit the Sleep Disorders Research Advisory Board for more information.
- National Sleep Research Resource (NSRR). This resource was established by the NHLBI to provide biomedical researchers a large, well-characterized data collection from NIH-funded sleep research studies. These data can be used in new research studies to advance sleep research, including research into circadian rhythm disorders. Visit the National Sleep Research Resource external link for more information.
Learn more about how the NHLBI is contributing to knowledge about circadian rhythm disorders.
- Helping to improve the health and well-being of shift workers. Shift work is known to increase the risk of several medical conditions, including cardiovascular disease, diabetes, metabolic syndrome, and obesity. We have funded research to help understand how disruptions in the sleep-wake cycle can cause these conditions. We have also supported research that uses computer analysis to help understand shift work disorder.
- Identifying the genes that control circadian rhythms. We have supported research into discovering the genes that control our circadian clocks and how these genes help us align our circadian rhythms with the environment. In 2017, researchers supported by several NIH Institutes, including the NHLBI, won the Nobel Prize in physiology or medicine for discovering several genes that control circadian rhythms. View Wake-up call: 2017 Nobel Prize in Medicine awarded for studies of the body’s internal clock for more information.
Summary of Disorders
Risk factors can include age, family history, environmental factors, stress and physical conditions.
Lying awake for a long time, sleeping for only short periods, waking up too early in the morning and/or having poor quality sleep.
Lifestyle changes can include - making bedroom sleep-friendly, going to sleep and waking up at same time everyday, avoiding caffeine, nicotine and alcohol, getting regular physical activity, avoiding daytime naps, eating meals on a regular schedule, limiting fluid intake close to bedtime, learning new ways to manage stress, and avoiding certain over-the-counter meds.
Psycholotherapeutic treatments can include –cognitive therapy, relaxation or meditation therapy, sleep education, sleep restriction therapy, stimulus control therapy.
Medical treatments can include – Benzodiazepines, Benzodiazepine receptor agonists, Melatonin receptor agonists, Orexin receptor agonists, sometimes antidepressants, antipsychotics and anticonvulsants are used, and Melatonin supplements
Obesity, large tonsils, endocrine disorders, neuromuscular conditions, heart or kidney failure, genetic syndromes, and premature birth
Reduced or absent breathing, known as apnea events, frequent loud snoring, gasping for air during sleep, excessive daytime sleepiness and fatigue, decreases in attention, vigilance, concentration, motor skills, and verbal and visuospatial memory, dry mouth or headaches when waking, sexual dysfunction or decreased libido, waking up often during the night to urinate
Healthy lifestyle changes include - Heart healthy eating, regular physical activity, aiming for healthy weight, healthy sleeping habits, and quitting smoking.
Breathing devices such as continuous positive airway pressure (CPAP) machine.
Oral devices including - Mandibular repositioning mouthpieces, tongue retaining devices
Implants including those that detect breathing and nerve stimulator.
Therapy for mouth and facial muscles called orofacial therapy.
Surgical procedures including – Tonsillectomy, Maxillary/jaw advancement and tracheostomy
Unwillingly fall asleep in middle of driving, eating or talking, sudden muscle weakness (cataplexy), vivid dream-like images or hallucinations, total paralysis just before falling asleep or just after waking (sleep paralysis), excessive daytime sleepiness, fragmented sleep and insomnia, automatic behaviors
Medications including Modafinil, Amphetamine-like stimulants, Antidepressants and Sodium oxybate (also called GHB)
Lifestyle changes including - taking short scheduled naps, maintaining regular sleep schedules, avoiding caffeine or alcohol before bed, avoiding smoking, exercising daily, avoiding large heavy meals right before bedtime, relaxing before bed and safety precautions particularly while driving.
Circadian rhythm or sleep wake cycle disorders
Genetic conditions, lifestyle issues like jet lag, environment or occupational factors, age, sex and other medical conditions like ASD and blindness
Consistent difficulty falling asleep, staying asleep, or both, excessive daytime sleepiness or sleepiness during shift work, fatigue and exhaustion, lethargy, decreased alertness and difficulty concentrating, impaired judgment and trouble controlling mood and emotions, aches and pains, including headaches, stomach problems, in people who have jet lag disorder
Healthy lifestyle changes, bright light therapy and melatonin
Since sleep is such a complex biological and psychological process, it should come as no surprise that there are many different kinds of disorders of sleep. These disorders have different symptoms, can be caused by a variety of different situational and biological issues, and can be treated in a variety of ways.
- Psychology by Jeffrey C. Levy; licensed CC BY 4.0
- Sleep Science and Sleep Disorders: National Heart, Lung, and Blood Institute; National Institutes of Health; U.S. Department of Health and Human Services. Public Domain
- Insomnia: National Heart, Lung, and Blood Institute; National Institutes of Health; U.S. Department of Health and Human Services. Public Domain
- Sleep Apnea: National Heart, Lung, and Blood Institute; National Institutes of Health; U.S. Department of Health and Human Services. Public Domain
- Narcolepsy Fact Sheet: National Institute of Neurological Disorders and Stroke; National Institutes of Health; U.S. Department of Health and Human Services. Public Domain
- Recognizing the symptom spectrum of Narcolepsy to improve timely diagnosis: A narrative review by Quaedackers, L., Pillen, S., & Overeem, S. licensed under CC-BY NC 3.0