Phases of Sleep
There are five phases of sleep.
Phase 1 – Light sleep, eyes move slowly, and muscle activity slows. This stage forms 4-5% of total sleep.
Phase 2 – Eye movement stops and brain waves become slower, with occasional bursts of rapid waves called sleep spindles. This stage forms 45-55% of total sleep.
Phase 3 – Delta waves begin to appear, intermingled with smaller and faster waves. It forms 4-6% of total sleep.
Phase 4 – The brain produces delta waves almost exclusively. It is very difficult to wake someone during phase 3 and 4, called “deep sleep.” There is no eye movement or muscle activity. People awakened while in deep sleep do not adjust immediately and often feel tired and disoriented for several minutes after they wake up. This forms 12-15% of total sleep.
Phase 5 – Breathing becomes more rapid, irregular and shallow, eyes jerk rapidly in various directions, and limb muscles become temporarily paralyzed. Heart rate increases, blood pressure rises, and males develop penile erections. It forms 20-25% of total sleep time.