Most people are surprised when they find out how complex the nightly sleep cycle really is. Let's travel with mr pillow through a typical eight-hour night: First, you shut your eyes to begin the night's sleep. Your brain waves slow slightly, and become more regular, but higher in voltage. These waves, known as alpha, are about eight to twelve seconds long and indicate you are relaxing, though still awake.

After several minutes of alpha waves, you enter Stage 1 sleep, marked by four to eight second-long theta brain waves. Your heart rate slows and stabilizes, and your breathing becomes shallow and regular. This stage of sleep is light, and if you were awakened at this stage, you might deny you were asleep, or say you were only "half-asleep." Stage 1 can last from ten seconds to ten minutes.

You then move to Stage 2 sleep, marked by the same theta brain waves, interspersed with spiked brain waves called K-complex, and bursts of wave activity called spindles. Stage 2 is the beginning of actual sleep, and lasts ten to twenty minutes. It's marked by a lack of movement and disengagement from the environment. After the first two stages, which take twenty to thirty minutes, you enter Stage 3 sleep, a combination of theta and delta brain waves. Delta waves are very slow, high-voltage waves.

Soon, the theta waves disappear and you enter Stage 4 sleep, marked by the delta waves. Your muscles are completely relaxed, your blood pressure drops, and your breathing slows. If you are awakened from Stage 4 sleep, you will be disoriented and groggy for several minutes. Stage 4 sleep is very important for restoration, growth, and boosting the immune system.

After thirty to forty minutes of Stage 4 sleep, you begin travelling back through Stages 3 and 2, approximately 90 to 110 minutes after you fell asleep. Rather than returning to Stage 1 sleep, you enter REM sleep, known by that name because of the rapid eye movements accompanying this stage.