Narcolepsy is a chronic, neurological sleep disorder with no known cause. It involves the body's central nervous system. Narcolepsy is a genetic disorder, but what causes narcolepsy is not yet known.

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 at inappropriate times and places, and sleep attacks may occur with or without warning.

Attacks can occur repeatedly in a single day, drowsiness may persist for prolonged periods of time, and nighttime sleep may be fragmented with frequent awakenings.