Sleep paralysis is a condition in which people experience the inability to move either when they are falling asleep or when they are waking up. The former is called hypnogogic or predormital sleep paralysis, while the latter is referred to as hypnopompic or postdormital sleep paralysis. Hypnogogic sleep paralysis occurs because when you are falling asleep your body is slowing relaxing, but if you remain aware or become aware during this process you may notice the inability to move. Hypnopompic sleep paralysis occurs when you become aware before your REM (rapid-eye movement) cycle has finished because during REM sleep your eyes move quickly and dreams occur but your muscles are still relaxed. Sleep paralysis may be accompanied by: the inability to speak for a few seconds to a few minutes, pressure or a sense of choking, and other sleep disorders. This condition occurs in up to as many as 4 out of every 10 people, and is usually noticed during the teen years. Men and women can both have sleep paralysis, and it often runs in families. Other factors that may contribute to sleep paralysis include: lack of sleep or changing sleep schedules, mental conditions (such as bipolar disorder) and other sleep disorders (such as narcolepsy), sleeping on your back, substance abuse, and use of certain medications. Most people do not need treatment for sleep paralysis, but some treatments include: improving sleep habits, using prescribed antidepressant medication to regulate sleep cycles, and treating any other mental or sleep disorders.