The 4 Stages of Sleep

Staying healthy requires a lot of sleep. As we sleep, our bodies repair muscles, grow bones, manage hormones, and organize memories.

There are different stages of sleep. The two types of sleep are REM and non-REM. When adults fall asleep, they usually start with NREM sleep.

There are three stages of NREM sleep: N1, N2, and N3. There used to be four stages, but now N3 and N4 are combined into just N3.

During sleep, we cycle through 90-120 minute cycles. In a typical night, we go through four or five of these. Sleep stages change throughout the night. Usually, the first half of the night is more NREM sleep, and the second half is more REM sleep.

This article will cover these sleep stages, sleep problems, and ways to sleep better.

What’s a Sleep Cycle?

During sleep, your body goes through different stages called sleep cycles. A cycle consists of four stages and lasts 90 to 120 minutes. Typically, adults sleep 7 to 8 hours a night, so they go through about four to five cycles.

It’s important to note that the stages do not always follow one another. Dreams, which occur during REM sleep, can occur at any time during the cycle. In some cases, we might not even start at Stage 1, and we might not move directly from Stage 3 to REM. Instead, we might go back to Stage 2 before reaching REM.

Many people begin REM sleep about 90 minutes after falling asleep. In the wake of REM, we usually go back to Stage 1 or 2 and begin a new cycle.

Typically, a cycle starts with Stage 1 or 2, then moves on to Stage 3. You may wake up briefly during the cycle, as well as spend periods of time in REM sleep. REM sleep periods are short at first, but they increase with each new cycle.

How Does Your Sleep Cycle Change with Age?

Here’s how your sleep changes as you get older:

Babies (0 to 12 months): When you’re a newborn, your sleep is kinda all over the place. You have Active sleep, which is like REM sleep, and Quiet rest, which is similar to non-REM sleep. You spend most of your time in Active sleep, waking up a lot for feeding. You need about 14 to 16 hours of sleep a day.

Toddlers (1 year to 3 years): Once you hit 1 year old, your sleep starts to settle down. You spend about 25% of your sleep in Stage 3 (deep sleep) and 25% in REM sleep. You’ll sleep for around 11 to 14 hours a day, with more of that time being in deep and REM sleep.

Pre-School and School Age (3 to 12 years): Like toddlers, kids in this age range spend a lot of time in Stage 3 sleep. They need around 9 to 13 hours of sleep a night, depending on how old they are. As they grow, their bodies need even more deep sleep.

Adolescents through Adulthood (12 years and beyond): Teenagers usually need about 9 hours of sleep each night. But as they become young adults, this might drop to 7 to 9 hours. By the time they’re 12, their sleep looks a lot like adults’, with most of it happening in Stages 2 and 3.

4 Stages of sleep

Sleep occurs in different stages, each with its own characteristics and functions. Let’s break down the stages to understand what happens during each phase.

NREM (Stage 1)

The first stage of the sleep cycle acts as a bridge between wakefulness and deeper sleep. It typically lasts for about five to 10 minutes.

During this phase, your brain activity slows down, and your body begins to relax. Heartbeat, eye movements, and breathing all decrease in pace. Despite these changes, if someone were awakened during this stage, they might not realize they were asleep.

NREM (Stage 2)

In general, NREM stage 2 lasts for about 20 minutes per cycle and accounts for about half of total sleep time. In this state, your sense of awareness of your surroundings decreases, and your body temperature drops. During this time, eye movements cease, breathing ceases, and heart rate and breathing slow down.

A characteristic of this stage is the emergence of sleep spindles, which are sudden bursts of brain wave activity. As the brain processes and filters new memories acquired during the day, sleep spindles help consolidate memory.

NREM (Stage 3)

Stage 3 of NREM sleep is also known as delta sleep, a deep stage of sleep marked by the presence of slow delta waves in the brain. During this stage, it can be difficult to awaken someone, and they may not respond to external stimuli. In order to restore and repair physical health, deep sleep is fundamental.

In deep sleep, muscles relax completely, blood pressure drops, and breathing slows down. People tend to sleepwalk during this stage, particularly children and young adults.

During NREM stage 3, declarative memories, such as factual information and personal experiences, are consolidated, helping you feel refreshed the next day.

REM Sleep (Stage 4)

REM sleep, or rapid eye movement sleep, is the fourth stage of the sleep cycle. Despite increased brain activity similar to wakefulness, voluntary muscles become paralyzed during REM sleep, preventing us from acting out our dreams. R

EM sleep typically begins approximately 90 minutes after falling asleep. Brain activity intensifies, breathing becomes faster and irregular, and eyes move rapidly. This stage is when most dreaming occurs and is essential for processing emotions and storing emotional memories.

As the brain cements information in memory during this phase of sleep, REM sleep also plays a crucial role in memory consolidation and learning.

Sequence of Sleep Stages

When you sleep, it doesn’t go in a straight line through the four stages. Here’s how it usually goes:

  1. You start with NREM stage 1 sleep.
  2. Then, you move into NREM stage 2.
  3. After that, it’s NREM stage 3.
  4. You go back to NREM stage 2 again.
  5. Finally, you enter REM sleep.

After REM sleep, you typically go back to NREM stage 2 before the cycle starts again. This cycle repeats about four to five times in a full night of sleep.

As the night goes on, the time spent in each stage changes. This pattern of cycles and stages during sleep is called sleep architecture. A sleep specialist might show you this information using something called a hypnogram, which is a graph made by measuring brain activity with an EEG.

Factors That Influence Your Sleep Pattern

Your sleep quality and the duration of each sleep stage can be affected by various factors. Sometimes, you might not smoothly transition through every stage of sleep.

Here are some things that can change your sleep cycles:

  1. Age: As you get older, you tend to spend less time in deep sleep and REM sleep.

  2. Mental health: Depression and anxiety can affect how well you sleep. Depression can increase REM sleep time but shorten the time it takes to enter the first REM cycle after falling asleep.

  3. Sleep disorders: Conditions like circadian rhythm disorders, sleep apnea, REM sleep disorder, sleepwalking, and narcolepsy can mess with your sleep cycles.

  4. Traumatic brain injury (TBI): If you’ve experienced a TBI, it can lead to fewer minutes of REM sleep, more wake-ups during the night, and overall less sleep.

  5. Medication and drugs: Certain substances like alcohol, barbiturates, and benzodiazepines can reduce the time you spend in REM sleep.

Sleep Disturbances

The American Academy of Sleep Medicine estimates that 70 million Americans have trouble sleeping every year. Sleep deprivation can lead to other health issues.

Here are some common sleep problems and how to deal with them.

1. Insomnia

Some people have trouble falling asleep, staying asleep, or both. The condition is called insomnia, and it can make you feel very tired during the day. Insomnia is usually treated with cognitive behavioral therapy (CBT).

In some cases, doctors will also prescribe medicines to help you sleep better. It might also help to improve your bedtime routine (like making sure your bedroom is cozy and quiet).

2. Sleep Apnea

Sleep apnea occurs when your throat becomes too narrow while you’re asleep. It can disrupt your sleep. The main treatment involves CPAP machines that allow you to breathe while you sleep. If that doesn’t work, there are other options like a different machine or even surgery. For mild cases of sleep apnea, you may use some anti-snoring devices or anti-snoring mouthpieces.

3. Restless Leg Syndrome

Sleeping is difficult when you have restless leg syndrome because you feel strange and uncomfortable in your legs. Fortunately, some medicines are available to help.

4. Shift Work Disorder

Working odd hours can interfere with your sleep schedule. You may feel tired during the day and have other health problems as a result. Try taking short naps when you’re tired, avoiding bright lights when you’re sleeping, and reducing your work hours if you can.

5. Narcolepsy

It is common for people with narcolepsy to feel sleepy during the day, and sometimes they fall asleep without warning. The condition can be difficult to handle, but there are medicines that can help. A good routine, eating healthy, and staying active may also help you sleep better.

What Happens When Sleep Stages Are Altered

When your sleep stages get messed up, you can have problems. You may fall into this trap if you don’t spend enough time in each stage or if you don’t cycle through them properly. Here are some things that might go wrong:

  • There might be a difficulty concentrating and learning.

  • You might have difficulty being creative.

  • Decision-making could become challenging.

  • It might seem more difficult than usual to solve problems.

  • You might have difficulty remembering things or recalling information.

  • Your emotions or behaviors might be harder to control.

You may also be at risk of the following if your sleep cycle is disrupted:

  • More pain is felt.

  • Feeling inflammatory in your body.

  • A rise in blood pressure.

  • Having a heart condition.

  • Weight gain or obesity.

  • Having a higher risk of getting diabetes.

  • You might have a lower quality of life overall.

To avoid these problems, it’s important to maintain a healthy sleep routine.

Tips For a Healthier Sleep Cycle

Here are some easy tips to help you sleep better:

  • Try to avoid using phones or computers before bedtime.
  • Spend some time outside during the day to get natural light exposure.
  • Maintain a regular bedtime and wake-up time.
  • Engage in some physical activity every day.
  • Avoid heavy meals before bedtime.
  • Avoid drinking alcohol close to bedtime.
  • Keep your bedroom cool and dark for a comfortable sleep environment.
  • Make sure you get enough sleep, because more sleep means better REM sleep.
  • If you consistently follow these tips, you can often improve your sleep.

Try these tips for a week and if you still have difficulty sleeping, seek help from your doctor. The doctor might suggest medication or other options, such as a sleep apnea device.


1. What happens if you’re deprived of REM sleep?

A lack of REM sleep can lead to decreased cognitive function and depression. Research on this topic is limited, but most doctors recognise that REM sleep is important for overall health.

2. Why do people wake up at 3 a.m.?

Nocturnal awakening, or waking up in the middle of the night, occurs for a variety of reasons. This could be caused by a need to use the bathroom, noises disrupting sleep, caffeine or alcohol consumed too close to bedtime, or stress or anxiety. Sleep disorders like sleep apnea, periodic limb movement disorder, or nocturnal seizures can also cause nocturnal awakenings.

3. What stage of sleep cycle is best to wake up to?

A REM cycle, which is a lighter phase of sleep, is usually the best time to wake up. This facilitates the transition to wakefulness. After waking up during NREM stage three, the deepest stage of sleep, you may feel groggy and experience sleep inertia, which is a temporary feeling of disorientation and mood decline.

Need professional help to diagnose and address your sleep problems? Schedule an online consultation with sleep specialist Dr. John Williams.

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