We normally become paralyzed and unable to move anything but our eyes when in rapid eye movement (REM) sleep -- which prevents us from ‘acting out’ our dreams. Most people are quite unaware that this happens, since they are asleep at the time! (See page one of this handout for a description of REM sleep).
However, that same paralysis, which normally should occur only in REM sleep, sometimes intrudes into wakefulness. Such may occur at times of awakenings (as a brief persistence of paralysis when we awaken from REM sleep). It also may happen as we are just dozing off but not fully asleep. It can be thought of as an awake brain in a body that transiently ‘got stuck’ in REM sleep.
It is not the same as still being asleep but dreaming that one is struggling to wake up. Instead, the person is wide awake during sleep paralysis and if unfamiliar with its benign nature, terrified by his or her sudden helplessness and complete inability to move. It feels like being ‘buried alive’. Nonetheless, sleep paralysis is harmless. It usually lasts less than a minute (although it can feel like much longer!). Touching the person who is experiencing sleep paralysis ‘breaks it’ instantly -- but such seldom happens, since the person cannot call out for help.
Many people who have no other sleep disorders experience sleep paralysis on a rare basis. It can be worsened by sleep deprivation. Sleep paralysis occurs more frequently in some people with narcolepsy -- a relatively common disorder causing sleepiness and in some cases, such other symptoms as attacks of muscle weakness triggered by strong emotions (cataplexy).
Also, some patients with Sleep Apnea may awaken with sleep paralysis, particularly if sleeping on their back. Both that position and REM sleep can make breathing worse-- resulting in sleep fragmentation with repeated arousals. Look for other signs of sleep apnea especially if you experience sleep apnea when sleeping on your back and if you have any of its other symptoms.