A neurologic disorder, narcolepsy is a derangement of the normal sleep-wake cycle characterized by episodes of excessive daytime sleepiness (EDS), cataplexy, hypnagogic and/or hypnopompic hallucinations, and sleep paralysis, all of which represent inappropriate intrusions of sleep into the awake state. Onset of this disorder may be at any time, from as young as 10 years of age through the fifth decade. There is no known cure at the present time.

Narcolepsy is found worldwide without regard to race or ethnic group. Some groups appear to be more prone to develop narcolepsy; in Japan the estimated incidence is 1:600, in the United States the estimated prevalence ranges from 1:1000 to 1:10,000, and in Israel the estimated prevalence is 1:500,000. The estimated prevalence rates for the United States, alone, may account for 10,000 to 20,000 to as many as 100,000 to 200,000 patients.

The cause of narcolepsy has not been delineated. The disease does seem to appear in families.