Sleep scientists estimate that most people should experience five sleep cycles per night, and, during these cycles, our bodies will move through different stages of NREM (Non-Rapid Eye Movement) and REM (Rapid Eye Movement) sleep. In order to get good, restorative sleep, we need to accomplish all five stages of sleep throughout the night. Certain sleep stages can even dictate what hormones are released and impact psychological functions such as empathy and mood. Here is a closer look at each stage of sleep:
- 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.
People go through all stages of sleep several times during the night. To be able to pass through all the stages of sleep – which we do several times per night – sufficient melatonin levels must be present in the body. Unfortunately, as we age, melatonin decreases. Plus environmental factors such as the blue light from electronics and caffeine can inhibit the release of melatonin, making sleep more difficult to come by.