There may be a physical cause for dreams in which you find yourself unable to move or sense anything; it is called sleep paralysis. During REM sleep when dreams are most frequent, your brain shuts down your body’s nerve impulses, notably to the limbs, to prevent you from acting out the drama of your dreams. However, should you gain some awareness during sleep paralysis, your unconscious mind may mirror your physical actions in your dream. There may also be a physical cause for some falling dreams; such dreams may be triggered by a muscular spasm called a myoclonic jerk that typically occurs just before you are fully asleep. Dreams in which you suddenly step into nothingness are believed to be associated with myoclonic jerks.
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