What are and what causes sleep disorders?
Sleep disorders are disruptions of the sleep cycle or the quality of sleep. About 50 to 70 million Americans are believed to suffer from chronic sleep disorders, with millions more affected on an occasional basis. Doctors have defined over 70 different types of sleep disorders, but the most common sleep disorders are insomnia, sleep apnea, restless legs syndrome, and narcolepsy.
- Insomnia is the perception of poor-quality sleep, including the inability to fall asleep or stay asleep. Because people differ in their need for sleep, there are no fixed criteria that define insomnia. Insomnia is very common and occurs in 30% to 50% of the general population. Approximately 10% of the population may suffer from chronic (long-standing) insomnia. Sleep onset insomnia is characterized as occurring at the beginning of the desired sleep time and lasting for greater than 30 minutes. Sleep maintenance insomnia is when individuals fall asleep, but awaken periodically or for lengthy periods during the night, increasing the wake-after-sleep-onset (WASO).
- Sleep apnea is another common sleep disorder characterized by a reduction or pause of breathing (airflow) during sleep. Central sleep apnea (CSA) occurs when the brain does not send the signal to the muscles to take a breath, and there is no muscular effort to take a breath. Obstructive sleep apnea (OSA) occurs when the brain sends the signal to the muscles and the muscles make an effort to take a breath, but they are unsuccessful because the airway becomes obstructed and prevents an adequate flow of air. Mixed sleep apnea occurs when there is both central sleep apnea and obstructive sleep apnea.
- Restless leg syndrome (RLS), also known as nocturnal myoclonus, is a type of sleep disorder characterized by uncomfortable sensations in the legs and an uncontrollable desire to move the legs. These abnormal sensations usually occur in the lower legs during the evening. Periodic leg movements (PLMs) are related to RLS, but occur after the onset of sleep and are labeled as a sleep disorder or syndrome when the movements cause increased activity in the brain. During the early stages of sleep, these episodes of leg movement often last up to an hour. The abnormal sensations of RLS are quite variable. They have been described as a crawling, creeping, pulling, drawing, tingling, pins and needles, or prickly discomfort. They are not cramping in character. Patients with RLS may have difficulty falling asleep because of the difficulty getting comfortable and an increased urge to move their legs. Many patients with RLS will have PLMs and vice versa, but they are not the same disorder.
- Narcolepsy is a disease of the central nervous system that results uniformly in excessive daytime sleepiness (EDS). Other primary symptoms of narcolepsy include the loss of muscle tone (cataplexy), distorted perceptions (hypnagogic hallucinations), and the inability to move or talk (sleep paralysis). Additional symptoms can include disturbed nocturnal sleep and automatic behaviors (affected persons carry out certain actions without conscious awareness). All of the symptoms of narcolepsy may be present in various combinations and degrees of severity.
Other sleep disorders include:
- periodic limb movement disorder
- REM sleep behavior disorder
- nightmares, and
- circadian rhythm disorders, and
- night shift work sleep disorder