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Sleep Cycles






Understanding the Different Stages of Sleep

Every night when we sleep, our body and mind go through phases. These phases are called sleep stages.

There are 4 sleep stages, 3 non-REM and REM. These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage. These 4 stages make up a sleep cycle. Typically, we have 4/5 sleep cycles each night.

Stage 1

This stage is essentially the “dozing off” stage and it is normally quite short, lasting from 1 to 5 minutes.

In this stage, the body hasn’t fully relaxed, but body and brain activities have started to slow with brief periods of movement (twitching). It is very easy to wake someone up at this stage, however if the person is left undisturbed, they can quickly move to stage 2.

Stage 2

In this stage, the person enters a more subdue state including a drop in temperature, relaxed muscles, and slowed breathing and heart rate. At the same time, brain waves show a new pattern and eye movement stops. Overall, brain activity slows, but there are short bursts of activity1 that actually help resist being woken up by external stimuli.

Stage 2 sleep can last for 10-25 minutes during the first sleep cycle, and each stage2 can become longer during the night. A person typically spends about half their sleep time in stage2 sleep.

Stage 3

Stage 3 is also known as deep sleep. It is hard to wake someone up in this stage. Muscle tone, breathing rate and pulse decrease at this stage as the body relaxes even more.

The brain activity during this stage has an identifiable pattern of what are known as delta waves. For this reason, stage 3 may also be called delta sleep or short-wave sleep (SWS).

Experts believe this stage is crucial to restorative sleep, allowing for bodily recovery and growth. It could also boost the immune system and other major bodily processes. there is evidence that deep sleep contributes to insightful thinking2, creativity3, and memory.

We spend the most time in deep sleep during the first half of the night. During the early sleep cycles, stage 3 usually last for 20-40 minutes. As you continue sleeping, these stages get shorter, and more time gets spent in REM sleep instead.



Stage 4

REM- rapid eye movement, in this stage brain activity picks up, getting close to levels of when we are awake. In this stage dreams occur. At the same time, our body experience atonia, which is a brief muscle paralysis, except for breathing muscles and the eyes. This happens to stop us acting out our dreams.

REM sleep is considered to be vital to cognitive functions4 like memory, learning, and creativity5.

Normally, you don’t enter a REM sleep stage until you’ve been asleep for about 90 minutes. As the night goes on, REM stages get longer, especially in the second half of the night. Although the first REM stage may last only a few minutes, later stages can last for 1hr. In healthy adults, REM stages should make up 25% of total sleep.


There are a few factors that can affect these stages such as:

· Age- newborns spend almost half of their sleep in REM and may enter this stage as soon as they fall asleep while elderly people spend a lot less time in REM sleep.

· Alcohol and some drugs can disrupt REM sleep and they can also change sleep architecture.

· Sleep disorders that cause multiple awakenings during the night such as sleep apnoea and restless leg syndrome(RLS) can disturb healthy sleep cycles.


These sleep stages are important because they allow the body to recover, repair and develop. Not getting enough deep and REM sleep can have a great impact on physical, mental and emotional health.

The best way to improve these stages is by having a sleep hygiene and having consistent sleeping and waking times.


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