Stages of Sleep: What Happens When You Sleep

You are probably aware of how important sleep is, but did you know that your body transitions through different cycles of sleep as your body rests, and each of these cycles plays an important role in the quality of our sleep, as well as the feeling of restoration or restfulness you feel when you’re awake? Throughout the night, your body will cycle through these stages several times.

What Are The Different Stages of Sleep?

There are four different stages of sleep that you go through during the night. Here is a look at each stage. 

Stage 1 - NREM

In the first stage of sleep, Non-Rapid Eye Movement (NREM) sleep stage 1, our body hasn’t fully relaxed yet as we are simply just beginning to doze off. The brain and body’s activities, however, are beginning to slow such as breathing, heartbeat, and eye movements. From time to time, the sleeper experiences moments of twitching and brief movements that usually occur within this first stage. 

Light changes in brain activity also occur during this stage of sleep. It is fairly easy to awaken someone who is in this stage of sleep, but if not disturbed the sleeper can then move rather quickly into the second stage of sleep. Stage one of the sleep cycle typically lasts about one to five minutes before we are actively moving into stage two.

Stage 2 - NREM

In this stage of the cycle, our bodies are experiencing a slowing in our breathing, as well as our heart rate. Our body’s temperature begins to drop and our muscles are further relaxed. Our brain activity begins to slow in this stage, as well. However, even with all of these physical tells of our body relaxing and “letting go,” as well as internally our brain quieting and slowing, too, the brain does experience short bursts of activity known as sleep spindles. 

This stage of sleep typically lasts around 10 to 25 minutes, however, each stage may become longer as the night progresses and the cycles repeat themselves. It is estimated that a sleeper spends about half of their time asleep in stage 2. Both stage 1 and stage 2 of the sleep cycle are stages of light sleep.

Stage 3 - NREM

This stage is when the sleeper enters a deep sleep. The body relaxes even further in this stage as breathing and pulse rate decrease, as well as muscle tone. 

During the first half of the night, the sleeper spends most of their time in this stage of deep sleep. Stage 3 commonly lasts 20 to 40 minutes, however, as the night progresses the sleeper will spend more time in the REM (Rapid Eye Movement) stage of sleep and less time in stages 1-3 of Non-REM sleep.

Stage 4 - REM

In stage four, the stage of sleep in which our body enters REM sleep, our body’s muscles experience a temporary paralysis known as atonia. The two exceptions to this muscular paralysis of course include the eyes (this stage is the rapid eye movement stage) and the muscles that control our breathing. Despite the individual being asleep, the brain’s activity levels are near what we would normally see when we are awake. 

The sleeper generally will not enter into REM sleep before they have been asleep for around 90 minutes or so. These stages of REM sleep do get longer as the night progresses, and while the first time the sleeper cycles through may only last a few minutes, later stages can last for as long as an hour.  

REM Sleep

REM sleep is marked by vivid dreams. And while dreams can occur throughout any stage leading up to this stage, they are less common and intense in any of the earlier stages. Researchers have hypothesized that the muscular paralysis a sleeper experiences in REM, atonia, may be a protective measure meant to stop sleepers from acting upon their dreams (and or nightmares) and unknowingly harming themselves or others in the process.  

REM sleep is important since it plays a vital role in our dreaming, emotional processing, memory, and healthy brain development. During REM sleep, it is believed that our dreaming may be involved in our emotional processing, as well as our brain processing and storing in memory things we may have learned or new motor skills we may have attained from the day before.

Sleep Facts

A major sleep fact to keep in mind when you consider your rest and how much you might need is that sleep deprivation can have a major impact on your mood and mental state. Apart from internal impacts from sleep deprivation, there are also outward and physical ones, as well. 

Sleep deprivation can cause issues with weight. Without enough rest you may even find yourself feeling drained or zapped of your energy. Sleep deprivation may also affect how quickly we heal (or do not.) 

Tips To Get More Quality Sleep

One somewhat obvious way that you can ensure you get more quality sleep is by limiting your time during your day that you are napping or dozing off. A nap may be okay from time to time, but be sure to try and limit the amount of naps, as well as the length.

Another way you can get better sleep is by limiting your screen time before bed. It is reported that some electronic devices emit a blue light that can disrupt the hormones your body utilizes to help you fall asleep.

It is important to remember a few key ways we can improve and enhance our sleep cycles, as well as our progression through each stage. You can ensure a consistent and regular sleep schedule by shutting off distractions that may keep you awake like your phone, TV, or anything else that may contribute to noise or light that could keep you awake.