Narcolepsy
Most people with narcolepsy also experience cataplexy, sudden muscular weakness without loss of consciousness, which usually accompanies laughter or anger. Other symptoms, occurring just after falling asleep or upon awakening, include sleep paralysis (a feeling that one cannot move) and vivid hallucinations.
The cause of narcolepsy is not known with certainty, and there is no cure. Treatment, including regular planned naps and the use of stimulant drugs (e.g., amphetamines) plus antidepressants for cataplexy, can help to control its symptoms.