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Stages of Sleep
Health

What Are the Stages of Sleep?

Tara Youngblood · Mar 23, 2022
Stages of Sleep

There are two types of sleep stages, NREM and REM. These types of sleep occur in four stages.

Here's how that works: As you sleep, your brain journeys through four stages of sleep of two different types.

Non-REM Sleep

Stages 1 through 3 are a type of sleep known as Non-Rapid Eye Movement (NREM) sleep. These stages are also described as quiet sleep.

REM Sleep

Stage 4 is a type of sleep known as rapid eye movement (REM) sleep. It's also known as active sleep.

Each stage of sleep plays a unique role in maintaining brain health and performance. Some stages power that ability of your brain and the rest of your body to make needed repairs and maintenance. You go through all four stages of sleep in a repeating cycle every night. Each repetition of the sleep cycle lasts longer and takes you into deeper sleep.

Wait. Aren't there five stages of sleep? The American Academy of Sleep Medicine used to recognize five, but sleep was redefined to four stages in 2007.

Adjust the Temperature tor Better Sleep

People fall asleep, stay asleep and feel rested based on their spectrum of different temperatures. Our sleep systems allow you to find the right temperature, ranging from 55-115º.

Learn More

What are the Stages of Sleep?

What's going on in the four stages of sleep? The Cliff Notes version of what happens during the four stages of sleep is something like this:

1. NREM (Stage 1 - Light Sleep)

For the first five to ten minutes, you go through a transition period from wakefulness to sleep. In Stage 1, your brain is still producing lots of high-amplitude theta waves. These theta waves are mostly generated in your frontal cortex, the "executive" center of your brain.

If someone wakes from this stage of sleep, you might tell them you were still awake, even though you weren't. Psychic phenomena are common in this stage of sleep.

You might experience a hallucination of some kind. It could be visual even with your eyes closed), or my likely auditory (even if you are wearing ear plugs). You can also have hallucinations involving taste or smell.

Your muscles may twitch suddenly or jerk violently. You may have the sensation of falling or spinning around. Usually, you won't remember these sensations when you wake up.

2. NREM (Stage 2 - Light Sleep)

For the next 20 minutes, your body temperature drops, Your heart begins to slow down. Both your pulse and your breathing become more regular. During Stage 2 sleep, you become less aware of your surroundings.

Your brain begins to produce a kind of wave known as "sleep spindles," an indication that is processing what you have learned during the day and forming new memories.

The American Sleep Foundation estimates that most people spend about half of their sleep time in Stage 2. This stage helps the brain slow down to enable the body to repair itself in NREM Stage 3.

3. NREM (Stage 3 - Deep Sleep)

In NREM Stage 3, your brain produces deep, slow delta waves, so many that this stage is known as delta sleep. During this stage of sleep, you probably won't be responsive to loud noises or changes in temperature.

It will be hard for someone to wake you up. Your brain produces growth hormone when you are in Stage 3 sleep. This is the hormone that stimulates the building of muscles and the burning of fat.

Because your body produces less growth hormone as you get older, not getting enough deep sleep causes weight gain. Your body also uses this stage of sleep to bolster your immune system.

NREM Stage 3 is also the time your brain forms declarative memories. This is the stage you need to be able to "sleep on" facts you have tried to memorize the day before, so you will remember them when you wake up.

Stage 3 sleep lasts 20 to 40 minutes.

Learn more on how to get more deep sleep

4. REM Sleep (Stage 4)

Stage 4 is rapid eye movement sleep. During this stage, your body becomes immobilized while your brain becomes almost as active as when you are awake. Your eyes move rapidly, even though your eyelids are closed as if you were seeing things in a dream world.

REM Sleep and Dreams

Dreams can occur in any sleep stage. They are often described as an array of feelings, emotions, and images. But, REM Sleep is known for the most vivid dreams as there is a significant uptick in brain activity.

Most of your dreaming occurs in REM Sleep. Fortunately, assuming you don't suffer from a disorder of arousal, like sleepwalking, your muscles are paralyzed, so you can't act out your dreams. Your brain processes emotions in Stage 4 sleep.

It assembles emotional memories in Stage 4 the same way it assembles factual memories in Stage 3. The first period of REM sleep lasts about 10 minutes, but your dream time gets longer and longer throughout the night.

Your Road to REM Sleep Takes Two Detours

You don't progress through these two types of sleep stages in an exact order. You begin sleep in NREM Stage 1. NREM Stage 2 follows NREM Stage 1, and then NREM Stage 3 follows NREM Stage 2. But you go back into NREM Stage 2, leaving the deepest stage of sleep, before you enter REM sleep, Stage 4, when you can dream.

After REM sleep is over, your brain returns to NREM Stage 2 to start the cycle all over again, 1-2-3-2-4-2-3-2-4 and so on. You will go through your entire cycle four or five times during eight hours of sleep.

If you were to spend the night hooked up to an EEG, it would record your sleep architecture, the exact stages of sleep you experience during the night and how long you experience them, in a recording called a hypnogram.

The Different Brain Waves 

A lot of what scientists know about the nature of sleep comes from studies of volunteer patients who spent the night in a sleep lab hooked up to an electroencephalograph, more commonly called an EEG. The neurons in your brain "talk" to each other through waves of energy.

EEG records five different speeds of brain waves. From the fastest waves in light sleep to the slowest waves in deep sleep, these types of brain waves are called:

  • Gamma
  • Beta
  • Alpha
  • Theta
  • Delta

When you are awake, your brain produces beta and gamma waves, the fastest kind of electrical communication between the neurons in your brain. As you start feeling drowsy, alpha waves take over. As you enter Stage 1 Sleep, theta waves begin to predominate, and there are even more theta waves in Stages 2 and 3.

When you finally enter REM sleep, in Stage 4, most of the neurons in your brain are firing very slowly. In Stage 4, your neurons are primarily generating delta waves.

What You Can Do to Improve Your Stages of Sleep

There are many ways to improve the stages of your sleep.

Sleep Temperature

However, the temperature is something that affects everyone's sleep, whether it’s sleeping cold or enjoying a warm cozy bed temperature. Keep in mind that people fall asleep, stay asleep and feel rested based on their spectrum of different temperatures.

Temperature & Sleep

69% of people reported that sleeping in a cold room strongly impacts their ability to sleep well.

Sleeping in a Warm Bed

When your bed is too warm, it's hard to fall asleep. You may stay awake until you are totally exhausted. Then you can finally fall asleep and complete Stage 1 sleep and move into Stages 2 and 3. But you will have problems again at Stage 4.

Sleeping in a bed that is too hot can make it harder for your body to lower your core temperature. This keeps you from entering Stage 4 REM sleep. That's the stage when you can dream and process how you feel about your day.

Sleeping in a Cold Bed

In a cooler bed, you sleep longer, because your brain can go through Stage 1 in just the usual five to ten minutes. You also enjoy better REM sleep, because your body can slow down so your brain can speed up. You wake up emotionally as well as physically refreshed.

Read More: Does Sleeping Cold Help You Lose Weight?

What Can Cause You to Lose Sleep?

There is a long list of specific conditions that cause some people to lose sleep: 

  • Sleeping next to a snoring bed partner, or being the person who does the snoring. Obstructive sleep apnea interrupts sleep dozens or even hundreds of times every night both for the person who has it and anyone who lives with them.
  • The need to get up to urinate at night.
  • Chronic pain, like arthritis and fibromyalgia.
  • Restless leg syndrome.
  • Anxiety, depression, and bipolar disorder.
  • Chronic health conditions like asthma, obesity, Alzheimer's, Parkinson's, and heart disease.
  • Excessive use of or addiction to stimulants such as caffeine and nicotine.

The answers for these conditions are usually something you need to work out with your doctor. Fortunately, not everyone has to deal with these impediments to a good night's sleep.

Citations/Resources:

Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of physiological anthropology31(1), 14. https://doi.org/10.1186/1880-6805-31-14

Van Cauter, E., & Plat, L. (1996). Physiology of growth hormone secretion during sleep. The Journal of pediatrics128(5 Pt 2), S32–S37. https://doi.org/10.1016/s0022-3476(96)70008-2

Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of physiological anthropology31(1), 14. https://doi.org/10.1186/1880-6805-31-14

An Approach for Clinical Pulmonology; Editors: Badr, M. Safwan (Ed.) 

About the Author

Tara Youngblood

Tara Youngblood

Tara Youngblood is ChiliSleep’s co-founder and CEO. An accomplished scientist, author, and speaker, Tara’s unique ideas are revolutionizing the future of sleep health by making sleep easy, approachable, and drug-free.
Learn more about Tara.

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