During each sleep cycle, the body goes through four main phases – Stages 1, 2, 3, and 4 – followed by a period called REM sleep (or Rapid Eye Movement). On average, it should take a person somewhere between 90 and 110 minutes to complete all phases of the cycle.
Sleep timing is controlled by what is known as the circadian clock. In humans, the circadian clock is an inner timekeeping device that acts to keep the body in a routine sleep pattern. Ever notice that person who regularly wakes up at an early hour will generally not be able to sleep much later than their normal waking time, even if they’re sleep-deprived? This is due to the circadian clock.
Regulated by this body clock, your nighttime journey consists of sleep cycles with specific sleep stages, all vital for your body. Understanding these sleeping needs, cycles and stages can help you get better sleep.
According to helpguide.org, these are the main phases of the natural sleep cycle and common characteristics of each:
• Stage 1 (Drowsiness) - Stage 1 lasts just about five or ten minutes. During this stage, your eyes move slowly under the eyelids, muscle activity slows down, and you are easily awakened.
• Stage 2 (Light Sleep) - Eye movements stop, heart rate slows, and body temperature decreases. Light sleep usually lasts 10 – 15 minutes.
• Stages 3 & 4 (Deep Sleep) - You’re difficult to awaken, and if you are awakened, you do not adjust immediately and often feel groggy and disoriented for several minutes. Deep sleep allows the brain to restore the energy expended during the day. Blood flow decreases to the brain in this stage, and redirects itself towards the muscles, restoring physical energy. Research also shows that immune functions increase during deep sleep.
• REM sleep (Dream Sleep) – At about 70 - 90 minutes into your sleep cycle, you enter REM sleep. You usually have three to five REM episodes per night. This stage is associated with processing emotions, retaining memories and relieving stress. Breathing is rapid, irregular and shallow, the heart rate increases, blood pressure rises.
It is important to understand and complete each stage of the sleep cycle in order to get the best sleep possible. Interrupting any of the above stages can leave you feeling even more tired than when you went to bed.