Stages of Sleep

Person sleeping in bed portraying the stages of sleep.

Have you ever wondered why you occasionally wake up feeling more tired than when you went to bed? Or why you wake up some days just because someone walked into your room, but others you have to snooze your alarm 6 times before being able to drag yourself out of bed? It all has to do with what stage of sleep you are in when you wake up. In this article, we will be going into more detail about the different stages of sleep.

REM and NREM sleep:

Scientists have divided sleep into two main categories; namely REM (Rapid Eye Movement) sleep, and NREM (Non-Rapid Eye Movement) sleep. REM sleep can then be further broken up into 3 stages. During the beginning of the night, you experience a longer period of NREM sleep, followed by a shorter period of REM sleep, but as the night progresses, the NREM sleep becomes shorter and the REM sleep increases. This cycle lasts about 90 to 110 minutes and is repeated roughly 4 to 6 times a night. It is important to note that each stage is characterised by different bodily responses, different functions, and the presence of different brain waves.

The four stages of sleep:

There are 4 stages of sleep:

  • The first NREM stage: Stage 1
  • Stage 2
  • The last NREM stage: Stage 3
  • REM sleep

Lets look at them in a bit more detail:

The first NREM stage (stage 1):

Baby yawning. Is this the onset of one of the stages of sleep?

The stage during which you fall asleep.

You close your eyes and your mind starts to grow quiet. You feel yourself drifting off to sleep, but any small disturbances can easily awaken you. Scientists consider stage 1 to be the transitional phase between being awake and being asleep, as it’s the first and lightest stage of NREM sleep. Your breathing slows down and slow eye movements can be observed. Your muscles start to release the tension from the day, often resulting in jerks or abrupt muscle spasms called hypnic myoclonia.

During this stage, your brain produces both low frequency and high amplitude alpha waves, as well as lower frequency and higher amplitude theta waves. The initial stages of stage 1 results in brain activity similar to that of someone who is awake and relaxed. Stage 1 takes 5 to 10 minutes.

Stage 2:

This stage is the first stage of genuine sleep.

Heart rate and body temperature drop and it is slightly more difficult to be awake during this stage. Muscle tone and muscle relaxation alternate and eye movement cease. Theta waves still predominate but are interrupted by sleep spindles ( bursts of higher frequency brain waves). Sleep spindles, as well as K complexes(sleep structures characterised by high amplitude patterns of brain activity that is triggered by external stimuli in the surroundings) are said to aid in the prevention of awakening. Approximately 20 minutes is spent in stage 2.

The last NREM stage (stage 3):

Person lying on bed. On her way to one of the stages of sleep.

Our deep sleep takes place in this stage.

This is the deepest of the NREM stages; waking up from this stage leaves you momentarily disoriented and confused. Stage 3 is broken up into two stages, but these stages are ultimately grouped together due to the fact that both are considered periods of low wave sleep (SWS). Brain activity slows down and high amplitude, very low-frequency delta waves predominate. Scientists claim that the higher your levels of alpha brain wave activity in your brain during this stage of sleep, the less awake and refreshed you feel after waking up.

The characteristics of this stage is: a further drop in blood pressure, deeper breathing and virtually no muscle movements. Hormones that trigger growth and replenishing of fatigued muscles, as well as hormones targeting appetite control are released during this stage, making it a necessary stage to rejuvenate and reboot your body for another day. You are typically found sleepwalkig, sleep talking and having night terrors in stage 3. You typically enter this stage 35 to 45 minutes after falling asleep.

REM sleep:

Your dreaming stage.

As the name suggests, rapid eye movement takes place during this stage. REM sleep is the stage where intense dreaming takes place, due to the heightened cerebral activity that occurs. Brain activity is high and resembles that of a person who is awake, which revitalises the brain and the body.

Another important part of REM sleep that you need to be aware of is that while heart rate and respiration increase drastically from the NREM stages, your limbs and muscles undergo temporary paralysis. The restriction of movement stops your body from acting out your dreams and potentially injuring yourself in the real world. REM sleep has been termed paradoxical sleep due to the opposing states of high brain activity and low muscle tone.

Waking up from REM sleep leaves you feeling extremely tired and groggy. REM sleep takes place 90 minutes after you fall asleep and the length varies for each cycle, starting at about 10 minutes and ending at approximately an hour in later cycles. An interesting comparison within REM sleep is that babies spend up to 50% of their sleep time in REM sleep, while adults typically only spend 20% of theirs in REM sleep.

The Sleep Cycle:

Little boys cuddling. Portraying the stages of sleep.

While the sleep cycle consists of only the 4 above-mentioned stages, it is not a linear process. The cycle typically goes as follows: stages 1, 2 and 3, then it reverses back to stage 2, and only then do you typically enter REM sleep. Furthermore, waking up occurs between stages or even during stages when you shift sleeping positions.

Every stage has unique characteristics and carries out different functions in the body; you need NREM sleep to rejuvenate and refresh your body, but you also need REM sleep to keep your mind active and healthy. All of the stages are necessary for the sleep cycle to function effectively and skipping any of the 4 stages could have dire consequences.

Waking up:

Empty bed. Stages of sleep, over.

When you wake up your heart rate and respiration return back to normal, and so does your muscle movement. You re-enter consciousness and, depending on how well you slept, feel ready to face another day of cognitive and physical exertion. Furthermore, you don’t only feel ready, but thanks to the sleep cycle, you are ready. What an intricate and interesting process…

And on that note, I think it’s time for bed…

Sleep well!

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