In some people, the walking, talking, and other body functions normally suppressed during sleep emerge during certain sleep stages.

Alternatively, the paralysis or vivid images usually experienced during dreaming may persist after awakening. These arousal malfunctions are collectively known as parasomnias and include confusional arousals, sleep talking, sleep walking, night terrors, sleep paralysis, and REM sleep behavior disorder (acting out dreams).

Most of these disorders - such as confusional arousals, sleep walking, and night terrors - are more common in children, who tend to outgrow them once they become adults. People who are sleep-deprived also may experience some of these disorders, including sleep walking and sleep paralysis. Sleep paralysis also commonly occurs in people who have narcolepsy.

Certain medications or neurological disorders appear to lead to other parasomnias, such as REM sleep behavior disorder, and these parasomnias tend to occur more in elderly people. If you or a family member has persistent episodes of sleep paralysis, sleep walking, or acting out of dreams, talk with your doctor.