Your Arms and Legs Are Paralyzed While You Dream

Dreams can be full of running and falling, yet the dreamer lies still. The U.S. National Institute of Neurological Disorders and Stroke explains why. There are two basic types of sleep: rapid eye movement, or REM, sleep and non-REM sleep. REM sleep first occurs about 90 minutes after falling asleep. During it, your eyes move rapidly from side to side behind closed eyelids. At the same time, according to the institute, your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams. The brain is busy meanwhile. During most stages of sleep a part of the brain called the thalamus becomes quiet, but during REM sleep it is active, sending the cortex the images, sounds and other sensations that fill our dreams. You cycle through non-REM and REM sleep several times in a typical night.