Five Stages of Sleep: What's Up While You're Down?

Waking Stage
Your body prepares for sleep. You're awake in this stage, but very relaxed. Your eyes can be open or closed.

Sleep Stage 1: Drowsiness
At this stage--lasting anywhere from 10 seconds to 10 minutes--you transition from being awake to falling asleep. Your breathing becomes shallow and irregular. People often say they are half-asleep in this stage. You respond fairly quicly to disturbances since you're still aware of your surroundings.

Sleep Stage 2: Light Sleep
During this stage, your eye movements come to a halt, your blood pressure drops, and your muscles relax more. This is the actual beginning of sleep, because at this point you're no longer aware of your environment.

Sleep Stage 3 & 4: Deep Sleep
In these two consecutive stages (four is slightly deeper), your body regenerates, repairs tissues, and develop bone muscle. Deep sleep also gives your immune system a boost and restores the energy you've lost during the day. You'll be in deep sleep for about 40 to 60 minutes. If you are woken up in the middle it'll take you about 20 seconds to realize where you are and what's happened.

Sleep Stage 5: REM (Rapid Eye Movement) Sleep
The first REM period is short, lasting about nine minutes. But as the night goes on, each successive REM period doubles in length. Your eyes will move rapidly in different directions and while your brain is shut off from the outside world, it's still working at preserving memory. You're also dreaming, and if you awaken you'll remember your dream vividly! In fact, many people will wake up during or just after REM sleep, either to roll over or to get up and start their day.