
REM sleep, the stage of sleep during which dreaming occurs, is characterized by paralysis of the voluntary muscles. Why? The phenomenon is known as REM atonia and prevents you from acting out your dreams while you're asleep. Basically, because motor neurons are not stimulated, your body does not move.
In some cases, this paralysis can even carry over into the waking state for as long as ten minutes, a condition known as sleep paralysis. Have you ever woken up from a terrifying dream only to find yourself unable to move? While the experience can be frightening, experts advise that it is perfectly normal and should last only a few minutes before normal muscle control returns.
