Narcolepsy is a disorder of the brain resulting in severe daytime sleepiness. Many patients also have cataplexy, which is a sudden loss of muscle tone caused by strong emotion such as anger, laughing or surprise.

Patients with narcolepsy may have sleep paralysis when they wake up and feel paralyzed.  This generally lasts a few minutes. Hypnologic hallucinations, or vivid life-like dreams occur just as the patient is falling asleep.

Narcolepsy may be diagnosed during sleep studies, which determine the degree of daytime sleepiness and presence of dreaming at the onset of sleep.