Sleep Stages

Sleep: Your body's means of rejuvenation - MayoClinic.com: "While sleeping, you move through six phases:

* Awake. It's normal to be awake for short periods during the night. Expect three to 10 brief arousals, though you probably won't remember each one. It's likely part of your body's defense mechanisms to keep you aware of what's going on around you.
* Stage one. During stage one, you sleep lightly and drift in and out of sleep. During this stage you're easily wakened. Your muscles begin to slow down and your eyes move very slowly.
* Stage two. In stage two, your muscles relax. Your brain waves slow down, though occasionally you have bursts of brain activity. You spend about half of your sleep in this stage.
* Stages three and four. Deep sleep sets in. Your brain waves become large and slow. Your breathing becomes rhythmic, and your muscles remain relaxed. At this point your body begins releasing reparative hormones. Stages one through four are referred to as non-rapid eye movement (NREM).
* Rapid eye movement (REM). During REM sleep your muscles stop moving completely. Your breathing and heart rate become rapid and irregular, your blood pressure is more variable, and your eyes move rapidly in bursts of activity. Your brain waves show a pattern similar to wakefulness. Scientists believe this indicates that your brain is using this time to sort and organize your memories. Dreaming takes place during this stage. If you're awakened during REM sleep, you may recall vivid dreams.

Throughout the night, you continuously move from one stage or type of sleep to another in cycles that can last from 70 to 90 minutes each. Early REM periods are very short, however, usually 5 to 10 minutes long. You may experience several longer REM periods as the night progresses."

My sleep study showed hundreds of arousals and very few periods of getting below level 2. Lack of REM sleep causes psychosis and death in mice; I shudder to think how much worse off I could have been. . .