A complete sleep cycle usually lasts 90 minutes and is comprised of five stages. Starting with light sleep and decreased brain activity, in stage two, eye movement and muscle activity stops, stages three and four is when deep sleep takes place, stage five is when Rapid Eye Movement and dreaming begins. At the end of the cycle, the sleeper returns to stage one to repeat the process throughout the night. Typically, normal restorative sleep requires five cycles per night. |