Everyone Experiences "Sleep Paralysis" Atleast Once

Almost everyone experiences "Sleep Paralysis" at least once. You're half conscious and cannot move but are fully aware of what's happening around.

Sleep paralysis is a feeling of being conscious but unable to move. It occurs when a person passes between stages of wakefulness and sleep. 

During these transitions, you may be unable to move or speak for a few seconds up to a few minutes. Some people may also feel pressure or a sense of choking.

Sleep paralysis may accompany other sleep disorders such as narcolepsy. Narcolepsy is an overpowering need to sleep caused by a problem with the brain's ability to regulate sleep.

Source: webmd.com