The 4 Stages of Sleep

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Raj Dasgupta, MD

Sleep is really important for staying healthy. When we sleep, our bodies do a lot of important stuff like fixing muscles, growing bones, managing hormones, and organizing memories.

Sleep comes in different stages. There’s REM sleep and non-REM (NREM) sleep. Most adults start with NREM sleep when they fall asleep.

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

Sleep happens in cycles that last about 90 to 120 minutes each. During a typical night, we go through about four or five of these cycles. Throughout the night, we move through different stages of sleep. Usually, the first half of the night has more NREM sleep, while the second half has more REM sleep.

In this article, we’ll talk about these sleep stages, sleep problems, and how to sleep better.

What’s a Sleep Cycle?

When you sleep, your body goes through different stages called sleep cycles. Each cycle includes four stages and lasts about 90 to 120 minutes. Most adults sleep for 7 to 8 hours a night, so they go through about four to five cycles.

Here’s the thing: the stages don’t always happen in order. REM sleep, which is when you dream, can happen at any time during the cycle. Sometimes we don’t even start at Stage 1, and we might not go straight from Stage 3 to REM. Instead, we might go back to Stage 2 before reaching REM.

For many people, REM sleep starts about 90 minutes after falling asleep. After REM, we usually go back to Stage 1 or 2, and a new cycle starts.

A typical cycle starts with Stage 1 or 2, then goes through Stage 3. During the cycle, there are times when you might wake up briefly, and there are periods of REM sleep. At the beginning, REM sleep periods are short, but they get longer 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)

NREM stage 2 comprises about half of total sleep time and usually lasts for around 20 minutes per cycle. Here, you become less aware of your surroundings, and your body temperature decreases. Eye movements cease, and breathing and heart rate stabilize.

This stage is characterized by the emergence of sleep spindles, which are rapid bursts of brain wave activity. Sleep spindles are believed to aid in memory consolidation, helping the brain process and filter new memories acquired during the day.

NREM (Stage 3)

Also known as delta sleep, NREM stage 3 is a deep sleep stage marked by the presence of slow delta waves in the brain. It is challenging to awaken someone during this stage, and they may not respond to environmental stimuli. Deep sleep is crucial for physical restoration and repair, with muscles completely relaxed, blood pressure lowered, and breathing slowed. Sleepwalking often occurs during this stage, particularly in children and young adults.

NREM stage 3 is vital for feeling refreshed the next day and for consolidating declarative memories, such as factual information and personal experiences.

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.

REM sleep is also crucial for memory consolidation and learning, as the brain cements information into memory during this phase.

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

Lots of people have trouble sleeping, about 70 million every year according to the American Academy of Sleep Medicine. Not being able to sleep well can cause other health issues. Let’s talk about some common sleep problems and how to deal with them.

1. Insomnia

Some folks find it hard to fall asleep, stay asleep, or both. This is called insomnia and it can make you feel really tired during the day. The main treatment for insomnia is something called cognitive behavioral therapy (CBT). Sometimes, doctors also give medicine to help you sleep better. And improving your bedtime routine (like making sure your room is cozy and quiet) might help too.

2. Sleep Apnea

Sleep apnea is when you stop breathing while you’re asleep because your throat gets too narrow. This can mess up your sleep. The main treatment is a machine called CPAP that helps you 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

Restless leg syndrome makes your legs feel weird and uncomfortable, especially when you’re trying to sleep. Some medicines can help, and having a good bedtime routine might make it easier to relax and fall asleep.

4. Shift Work Disorder

If you work odd hours, your sleep schedule might get messed up. This can make you tired during the day and cause other health problems. Taking short naps, avoiding bright lights when it’s time to sleep, and maybe working fewer hours can help.

5. Narcolepsy

Narcolepsy makes you really sleepy during the day, and you might even fall asleep without warning. It can be tough to deal with, but there are medicines that can help. Having a good routine, eating healthy, and staying active might also make it easier to sleep better.

What Happens When Sleep Stages Are Altered

When your sleep stages get messed up, it can cause problems. This can happen 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:

  • Learning and focusing might become harder.
  • You might find it difficult to be creative.
  • Making smart decisions could become a challenge.
  • Solving problems might seem more difficult than usual.
  • Remembering things or recalling information might be tough.
  • It might be harder to control your emotions or behaviors.

If your sleep cycle is disrupted, you could also be at risk for:

  • Feeling more pain.
  • Experiencing inflammation in your body.
  • Developing high blood pressure.
  • Having heart problems.
  • Gaining weight or becoming obese.
  • Being more likely to get diabetes.
  • Your overall quality of life might go down.

So, it’s important to try to maintain a healthy sleep routine to avoid these issues.

Tips For a Healthier Sleep Cycle

Here are some easy tips to help you sleep better:

  1. Cut down on screen time: Try to avoid using phones or computers before bedtime.
  2. Soak up some sunlight: Spend some time outside during the day to get natural light exposure.
  3. Stick to a schedule: Go to bed and wake up around the same time every day.
  4. Stay active: Get moving each day with some exercise.
  5. Watch what you eat: Avoid heavy meals right before bedtime.
  6. Skip the nightcap: Try not to drink alcohol close to bedtime.
  7. Create a comfy sleep environment: Keep your bedroom cool and dark.
  8. Get enough sleep: Aim for a full night’s rest, as more sleep means more quality REM sleep.

If you consistently follow these tips, you can often improve your sleep.

If you still struggle with sleep after trying these tips for a week, consider talking to a doctor for further advice. They might suggest medication or other solutions like a sleep apnea device.


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

Not getting enough REM sleep can lead to decreased cognitive functioning and increased rates of depression. There’s not a lot of research on this topic, but it’s important to ensure you’re getting adequate REM sleep for overall well-being.

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

Waking up in the middle of the night, known as nocturnal awakening, can happen for various reasons. It could be due to needing to use the bathroom, noises disrupting sleep, consuming caffeine or alcohol too close to bedtime, or feeling stressed or anxious. Nocturnal awakenings can also be caused by sleep disorders like sleep apnea, periodic limb movement disorder, or nocturnal seizures.

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

It’s usually best to wake up during an REM cycle, which is a lighter phase of sleep. This makes the transition to wakefulness easier. Waking up during NREM stage three, the deepest stage of sleep, can leave you feeling groggy and may result in sleep inertia, which is a temporary feeling of disorientation and mood decline after waking up.

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

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