The exact cause of narcolepsy is not known. An abnormality in the chemistry regulating sleep and wakefulness in the brain is suspected, but not proven. Both genetic and environmental factors are believed to play a role in the development of this disorder. Sleep attacks are short periods of sleep that occur many times a day, regardless of the amount or quality of sleep the night before. They are often described as irresistible and may occur with or without warning when a person is driving, working, eating, talking, or engaging in any other activity.
Most patients also experience persistent daytime drowsiness.
Excessive daytime sleepiness is usually the first symptom of narcolepsy and often the most difficult symptom to control. Cataplexy refers to sudden, brief episodes of muscle weakness or paralysis triggered by strong emotions such anger, laughter, surprise or anticipation. Although unable to move, the person remains conscious. For some people, any strong emotion may trigger cataplexy, while others react to only certain specific emotions. Although most patients experience cataplexy, some patients never develop this symptom.