One way to divide the different stages of sleep is into REM and NREM sleep. REM is when most of what most people would call dreams occur. It is important to note that REM is not the only stage at which dreams can occur.6 REM sleep is associated with muscle atonia (paralysis of voluntary musculature), gating of sensory input, rapid eye and middle ear movements, as well as heart rate and respiration changes (Carskadon & Dement, 1989; Symons, 1993).7 Muscle atonia is crucial during REM, because otherwise we would act out our dreams.