Sleep can be divided into rapid eye movement (REM) sleep when you have dreams, and sleep during which your eyes don't move, called non-REM sleep. The deeper stages of non-REM sleep are also referred to as restorative sleep. Healthy adults who sleep 8 hours a night will spend approximately 6 hours in non-REM sleep and 2 hours in REM sleep. Sleep generally occurs by moving through a series of stages, starting with the lightest: Stage 1 of non-REM sleep; moving to deeper stages of non-REM sleep; and, finally, to REM, or dream, sleep. It's easy to be roused during the lighter stages of sleep. If you wake up during Stage 1, you'll probably feel as if you haven't slept at all. This is often the stage people experience when they fall asleep in front of the television. When you wake them up, they might say, "I wasn't sleeping. I was just resting my eyes."
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.
Sleep can be divided into rapid eye movement (REM) sleep when you
have dreams, and sleep during which your eyes don't move, called
non-REM sleep. The deeper stages of non-REM sleep are also referred
to as restorative sleep. Healthy adults... More