September 08, 2020 3 min read

The health benefits of a good night of rest are profound. It helps us rejuvenate and recharge, ensuring that our minds and bodies are ready to conquer whatever comes our way! Sleep, however, is not just a single long process, but rather a series of several phases that we go through. What differentiates one stage from the next is the variation in brain activity, which can be observed using an electroencephalograph or EEG device. Currently, it is well accepted that all of us go through five stages of sleep. Sleep can be broadly classified into two stages - NREM Sleep and REM Sleep. 

Non-Rapid Eye Movement (NREM)

Also referred to as NREM, it collectively includes the first four stages of sleep. As the name suggests, there is very little or no eye movement during this stage of sleep. NREM is often collectively called quiescent sleep, since there is almost no dreaming, and you are still able to move your muscles, unlike in REM sleep.

NREM Sleep Stage 1

The first stage of sleep is a transitional phase, where you find yourself flitting in and out of consciousness. During this stage, it is possible to be partially awake, and you find your mind slowly drifting off. Once you have drifted off to sleep, this stage ends. The first phase of sleep is the one in which you experience hypnic myoclonia, the falling sensation that jolts you awake.

NREM Sleep Stage 2

The second stage of sleep is one of the lighter stages of sleep. The body goes into a state of relaxation with the brain waves slowing down and eye movement completely halting. Brief bursts of brain activity called sleep spindles still occur and have been shown to be incredibly important for memory and learning. Despite being a light sleep stage, your body temperature drops, and the heart rate begins to slow down. Breathing and muscle tone are also relaxed during this phase.

NREM Sleep Stage 3

The third stage of sleep is a transitional phase towards very deep sleep from the lighter stages. This stage is a period of slow-wave sleep, commonly referred to as SWS, and is characterized by brain waves called Delta Waves that have a low frequency and high amplitude.

NREM Sleep Stage 4

Sleep stage 4 is the deepest phase of sleep. It is the most difficult to wake up from. If you are woken up during deep sleep, it is highly likely that you are groggy and disoriented for several minutes afterward. This stage is also part of slow-wave sleep. As you go from stage 3 to stage 4 of sleep, Delta Waves become the norm in this phase, and faster waves reduce drastically, although they aren't completely eliminated.

The fourth phase of sleep is what rejuvenates the body. Blood flow to the muscles is significantly improved providing them with much-needed nutrients and oxygen and aid in their recovery. Additionally, several important hormones are released during this stage which are critical for good health.

  • Growth hormones are produced by the body during deep sleep. It is estimated that nearly 75% of Human Growth Hormone (HGH) is released during sleep. HGH and other growth hormones help repair the muscles and tissues that were broken down during the course of the day. This is all the more important to athletes and individuals who exercise regularly since this is the time during which recovery occurs. This is why good sleep is crucial for athletic performance, strength, and coordination.
  • Appetite control hormones such as Leptin and Ghrelin are also released during this period. These hormones are essential to control excessive hunger. One of the effects of the lack of sleep is obesity, owing partially to the diminished production of these much-needed hormones.

Your blood pressure decreases even further in this stage, and breathing becomes slower, deeper, and more rhythmic. There is absolutely no eye movement in this phase, and the body is completely immobile. The lack of muscle movement, however, does not mean that the muscles do not have the ability to function. Usually, nightmares and bedwetting in children occur during this phase of sleep.