Sleep paralysis is a form of paralysis that occurs when a person is suddenly unable to move or speak for a few seconds or minutes, either when falling asleep or waking up. In the time between falling asleep and waking up, some people may also feel a sense of choking. Sleep paralysis may accompany other sleep disorders such as narcolepsy, an overpowering need to sleep caused by a problem with the brain's ability to regulate sleep.
Attribution: Straight Talk Foundation