Narcolepsy is characterized by uncontrollable sleep attacks during the day, extreme sleepiness, falling asleep during an activity, losing muscle tone due to feelings of anger, surprise, amusement, or stress. This condition can be especially dangerous if the event occurs while the person is driving or operating heavy machinery. One cause, however, is a brain disorder called narcolepsy. Narcolepsy, caused by an abnormality in the brain's control of the sleeping and waking states, may cause muscle weakness, awakening with a sensation of paralysis, or dreaming while awake. This disorder is treated with a variety of medications.