Sleepwalking can occur during the deep sleep you experience before REM sleep. Once you're in dream sleep, you can no longer move. Some experts believe this temporary paralysis during dream sleep is the body's natural defense to keep people from acting out their dreams while they are asleep.
In general, people spend approximately 90 minutes in non-REM sleep before REM sleep begins. They continue to move through this cycle of light, to deep, to REM sleep, and back to light sleep again throughout the night. You may hear people say, "I was in a deep sleep all night," but everybody actually shifts between light and deep sleep several times each night.
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