Every night people around the world climb into their beds, close their eyes and sleep. The phenomenon is something we are all very familiar with, but how exactly does it work? Up until the 1950s, scientists believed that sleep was just a passive period of unconscious rest, but we now know that it’s a complex process that is essential to the rejuvenation of our bodies and minds.
During sleep, your body moves through five different stages of both REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. Over the course of the night, your body will go through this five-stage cycle four to six times, spending an average of 90 minutes in each stage.
Each stage of sleep serves a unique restorative function, including muscle recovery, hormone regulation, and memory consolidation, making it essential to allow enough time to cycle through all sleep stages. Without a full night of sleep, your body and mind are deprived of the essential elements needed to help you get through the day.
- Stage 1 – This is the lightest stage of sleep, the transition phase, where you feel yourself drifting off. In the morning, if you didn’t set your alarm clock and woke up naturally, Stage 1 sleep would be the last stage before you fully wake up. You typically spend just five to ten minutes in Stage 1 sleep – just enough to allow your body to slow down and your muscles to relax.
- Stage 2: Amounting to 45% to 55% of your total sleep each night, this is the first real stage of sleep: conscious awareness of your external environment disappears. Stage 2 sleep is still considered light sleep. Your brain activity starts to slow down, as well as your heart rate and breathing. Your body temperature falls a little and you’re beginning to reach a state of total relaxation in preparation for the deeper sleep to come.
- Stage 3: This is the start of deep sleep, also known as slow wave sleep. During Stage 3, your brain waves are slow “delta waves,” although there may still be short bursts of faster of brain activity (also known as beta-waves). If you were to get awakened suddenly during this stage, you would feel groggy and confused, and find it difficult to focus at first.
- Stage 4: Of the five stages of sleep, this is the one when you experience your deepest sleep of the night. Your brain only shows delta-wave (slow wave) activity, and it’s difficult to wake someone up when they’re in Stage 4 of sleep. This cycle is critical because your body heals and repairs itself during this period. Additionally, your immune system is most active. Unfortunately, if you miss this important stage, you are more susceptible to infections, and likely to feel sleepy throughout the day.
- Stage 5: This is the stage of sleep when you dream. It is also referred to as “active sleep” or REM sleep, which stands for the rapid eye movements that characterize Stage 5. During REM sleep, your blood flow, breathing, and brain activity increases. The first period of REM sleep of the night usually begins about 90 minutes after you start drifting off and lasts for about 10 minutes. As the night passes, the periods of REM sleep become longer, with the final episode lasting an hour or so.