Explore Sleep Cycle Stages: What Happens in Each One?

When you sleep, your body and mind go through different stages to rest and heal. Each stage has its own unique role. All these four stages complete what’s called the sleep cycle.

In this article we are gonna discover the sleep cycle stages and what exactly happens in each one individually.

What is a sleep cycle

Sleep cycle is a pattern of sleep stages that happens during sleep. Sleep is divided into two main types: rapid-eye movement (REM) and non-rapid-eye movement (NREM). NREM sleep is divided into three stages: N1, N2, and N3.

look at this table for more explanation:

How many sleep stages are there?

There are four stages of sleep as we explained earlier three of them are NREM and the last one is REM.

Sleep cycle stages

But what happens in each stage? Let’s find out.

NREM Sleep Stages

NREM this name (Non-rapid eye movement) is used to describe the sleep stages that don’t involve rapid eye movements and it has three stages.

NREM Stage 1

NREM Stage 1 which is also known as N1, this is the first stage of non-rapid eye movement, this occurs when a person first falls asleep when your heart starts to slow down its beats and your body temperature starts to drop.

It is the lightest sleep between all three stages and it’s very easy to wake someone and it lasts between 1 minute and 7 minutes as the night moves on. 

You start to spend less time in this stage if the person is uninterrupted.

NREM Stage 2

NREM Stage 2 which is also known as N2, this is the second stage of the NREM type, you begin to enter a deeper level of sleep. 

Your breathing and heartbeat slow down even more, your body temperature drops and your muscles start to relax.

A person spends about 45%-55% of his sleep time during this stage among many cycles, it takes up to 25 minutes and it becomes harder to wake up the person in this stage.

This stage is still considered as light sleep but it’s not as light as N1. Nevertheless, this sleep stage is also marked by the appearance of two unique types of brain activity: 

Sleep Spindles: Which are short bursts of brain activity lasting 0.5 to three seconds for a few seconds. These spindles are believed to be linked with the process of memory consolidation

K-complexes: consist of a single sharp peak in electrical activity, they are also thought to play a role in protecting sleep integrity by suppressing external stimuli.

NREM Stage 3

NREM Stage 3 which is also known as Deep sleep, this is a stage where your heartbeat temperature, brain waves, and muscle activity will be at their lowest.

Scientists claim it to be the most critical stage for regenerating your body and brain. 

SWS is another name for stage 3 which refers to slow-wave sleep, the majority of brain waves during this stage are called delta waves, large and slow frequency waves.

During this stage, the body and the brain regenerate to be fully prepared to perform the next day. Here is some of what happens: 

  • Muscle Repair: N3 sleep is strongly linked with the release of growth hormone, which is responsible for muscle and bone growth and repair.
  • Immunity System: Deep sleep supports immune functioning. The body produces cytokines during sleep, which are proteins that help regulate the immune response.
  • Memory Processing: N3 sleep is essential for memory consolidation, where the brain processes and stores information gathered throughout the day.
  • Hormone Balance: Deep sleep helps regulate the balance of various hormones such as cortisol, insulin, and testosterone.

REM Sleep Stage

REM Sleep which is also known as Rapid eye movement, the name comes from how your eyes move behind your eyelids while you’re dreaming, most dreams occur during REM sleep.

This is a stage that may play a role in your learning, memory consolidation, mental well-being, emotional processing, and overall mood.

In REM sleep, there is rapid movement behind your closed eyes, an acceleration in your heart rate, and irregular in your breathing patterns.

Your brain activity looks very similar to brain activity while you’re awake, also many things happen in this stage like dreams, nightmares, and sleep paralysis (which is a feeling of being aware of everything around you but can’t move).

What does a healthy sleep cycle look like?

A healthy sleep cycle is an uninterrupted cycle when you go through all 4 stages of sleep uninterrupted means there is not too much noise or light in the room, 

One completed sleep cycle takes around 90-120 min and you need about 4-6 sleep cycles per night.

Which sleep stage is most important?

Deep sleep is the stage where you get all the benefits from your sleep, you basically regenerate your physical and mental wellbeing.

During this stage, the body repairs tissues, stimulates growth and development, and strengthens the immune system. It plays a major role in maintaining your health.

How Much Deep Sleep Do You Need? 

Average adults need about 7-8 hours of sleep, 25% of them should be deep sleep, so you are talking about 1:30-2 hours of deep sleep per night.

As you get older the amount of deep sleep you get may decrease so you should be prioritizing your sleep even more.

What stage of sleep is best for waking up from?

The best stage of sleep to wake up from is typically during a lighter stage of sleep, specifically during non-rapid eye movement NREM Stage 1 or NREM Stage 2. 

Waking up during Stage 3 (deep sleep) or waking up during rapid eye movement (REM) is linked with something called sleep inertia, which is a period of grogginess and reduced cognitive performance. 

What are the causes of lack of deep sleep?

There are several factors for the lack of deep sleep:

  • Anxiety and stress: stress is the enemy of relaxation.
  • Poor sleep environment: excessive noise, bright lights, or an uncomfortable room temperature.
  • Caffeine and alcohol consumption: consuming caffeine before sleep time may not be a good idea, try not to consume caffeine 6 hours before bed and try to avoid alcohol completely because it’s bad for your health. 
  • Age: As you get older, you will spend less time in deep sleep.


In conclusion, going through the intricate world of sleep stages reveals a fascinating journey that our minds experience every night. 

Embracing the significance of sleep stages prompts a reevaluation of our lifestyles and habits. 

Prioritizing quality sleep is a fundamental investment for your physical and mental health.


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