Narcolepsy is a chronic sleep disorder with no known cause. The main characteristic of narcolepsy is excessive and overwhelming daytime sleepiness, even after adequate nighttime sleep. A person with narcolepsy is likely to become drowsy or to fall asleep, often at inappropriate times and places. Daytime sleep attacks may occur with or without warning and may be irresistible. These attacks can occur repeatedly in a single day. Drowsiness may persist for prolonged periods of time. In addition, nighttime sleep may be fragmented with frequent awakenings.
Three other classic symptoms of narcolepsy, which may not occur in all patients, are:
Cataplexy:
sudden episodes of loss of muscle function, ranging from slight weakness (such as limpness at the neck or knees, sagging facial muscles, or inability to speak clearly) to complete body collapse. Attacks may be triggered by sudden emotional reactions such as laughter, anger, or fear and may last from a few seconds to several minutes. The person remains conscious throughout the episode.
Sleep paralysis:
temporary inability to talk or move when falling asleep or waking up. It may last a few seconds to minutes.
Hypnagogic hallucinations:
vivid, often frightening, dream-like experiences that occur while dozing or falling asleep.
Daytime sleepiness, sleep paralysis, and hypnagogic hallucinations can also occur in people who do not have narcolepsy.
In most cases, the first symptom of narcolepsy to appear is excessive and overwhelming daytime sleepiness. The other symptoms may begin alone or in combination months or years after the onset of the daytime sleep attacks. There are wide variations in the development, severity, and order of appearance of cataplexy, sleep paralysis, and hypnagogic hallucinations in individuals. Only about 20 to 25 percent of people with narcolepsy experience all four symptoms. The excessive daytime sleepiness generally persists throughout life, but sleep paralysis and hypnagogic hallucinations may not.
The symptoms of narcolepsy, especially the excessive daytime sleepiness and cataplexy, often become severe enough to cause serious disruptions in a person’s social, personal, and professional lives and
How Common Is Narcolepsy?
Although it is estimated that narcolepsy afflicts as many as 200,000 Americans, fewer than 50,000 are diagnosed. It is as widespread as Parkinson’s disease or multiple sclerosis and more prevalent than cystic fibrosis, but it is less well known. Narcolepsy is often mistaken for depression, epilepsy, or the side effects of medications.
Who Gets Narcolepsy
Narcolepsy can occur in both men and women at any age, although its symptoms are usually first noticed in teenagers or young adults. There is strong evidence that narcolepsy may run in families; 8 to 12 percent of people with narcolepsy have a close relative with the disease.
What Happens In Narcolepsy?
Normally, when an individual is awake, brain waves show a regular rhythm. When a person first falls asleep, the brain waves become slower and less regular. This sleep state is called non-rapid eye movement (NREM) sleep. After about an hour and a half of NREM sleep, the brain waves begin to show a more active pattern again, even though the person is in deep sleep. This sleep state, called rapid eye movement (REM) sleep, is when dreaming occurs.
In narcolepsy, the order and length of NREM and REM sleep periods are disturbed, with REM sleep occurring at sleep onset instead of after a period of NREM sleep. Thus, narcolepsy is a disorder in which REM sleep appears at an abnormal time. Also, some of the aspects of REM sleep that normally occur only during sleep–lack of muscle tone, sleep paralysis, and vivid dreams–occur at other times in people with narcolepsy. For example, the lack of muscle tone can occur during wakefulness in a cataplexy episode. Sleep paralysis and vivid dreams can occur while falling asleep or waking up.