Narcolepsy is a chronic, neurological sleep disorder that is characterized by excessive daytime sleepiness, cataplexy, and abnormal intrusion of REM sleep into wakefulness. Individuals with narcolepsy are so overwhelmed by sleep that they may fall asleep at odd or inappropriate times such as during work, school, or other important engagements. Although a brief nap may provide temporary relief, the sensation of sleepiness inevitably returns. Many patients with narcolepsy also experience cataplexy which is characterized by a sudden feeling of weakness or paralysis in the head, legs, or other body parts in response to some form of excitement or laughter. Ironically, individuals with narcolepsy have poor quality nighttime sleep. The symptoms that are associated with narcolepsy are thought to occur due to dysregulation of REM sleep. Thus, individuals with narcolepsy may also experience brief episodes of being unable to move when waking up (sleep paralysis) as well as vivid visual hallucinations while falling asleep.