Stages of Sleep: Understanding REM and Non-REM Sleep Cycles

Ryan Fiorenzi, BS, Certified Sleep Science Coach - Updated on March 22nd, 2023

The 4 Sleep Stages

Most people go through 4 or 5 sleep cycles per night. Each cycle has 4 stages, with the first 3 being non-REM (rapid eye movement):

  • Stage 1—Where you transition from being awake to being asleep. It's when your heartbeat, breathing, and eye movement slow. Your muscles may also twitch as you sink deeper into sleep towards stage 2. You can be woken up easily at this stage. Your brainwaves are in the alpha state.
  • Stage 2—Your heart rate and breathing slow even further, your temperature drops and eye movement ceases. Brainwaves are limited to brief bursts of theta activity.
  • Stage 3—This is the stage of deep sleep that gives you a feeling of being refreshed in the morning. This is the stage where it would be the hardest to wake you up. Your breathing and heartbeat are at the lowest levels at this point, your muscles are very relaxed, and brainwaves are in the delta wave state, which is even slower than in stage 2. This stage is where many parasomnias occur, such as sleepwalking and night terrors. It's also the stage where human growth hormone is released and your immune system is restored.
  • REM (rapid eye movement)—This stage is where most dreaming occurs, and where memory consolidation happens. Your eyes move from side to side quickly, but you're unable to move your legs and arms, which prevents you from acting out your dreams. Your heartbeat and breathing increase and your brain is almost as active as it is during wakefulness. It's easier to wake you from this stage of sleep, and if awakened, you'll feel groggy. This is also the stage where erections occur in males, and the body loses its ability to regulate temperature.

How Long Are Sleep Cycles and Each Stage?

Most sleep cycles range between 90 to 120 minutes per cycle, with the first one being around 90 minutes, and the subsequent ones ranging from 100 to 120 minutes. The breakdown at every stage is as follows:

  • Stage 1—10 minutes
  • Stage 2—54 to 72 minutes
  • Stage 3—5 to 14 minutes
  • Stage 2—54 to 72 minutes

The Function of the Different Brainwaves

There are four categories of brainwaves, or frequencies, listed from most active to least active.


  • 15-40 cycles/second

This is the fastest of the four brainwaves and is characteristic of someone who is intensely engaged in an activity, such as a teacher running a classroom or a boxer in a fight.


  • 9-14 cycles/second

Whereas beta is a state of arousal, alpha is non-arousal. These are a greater amplitude and slower frequency. A person in this state may be resting, meditating, or enjoying a sunset.


  • 5-8 cycles/second

A person in the theta state is often daydreaming. People doing a repetitive task often enter this state and can't recall what exactly they were doing for the last few minutes. Taking a shower, driving to work, or other automatic activities may bring on this state. This mental state is where ideas flow freely without judgement or guilt and it is often why people come up with creative ideas while doing automatic tasks such as taking a shower.


  • 1.5-4 cycles/second

This is the slowest of the four brainwaves and is characteristic of deep, dreamless sleep where there's no external awareness. It never goes down to 0, unless the person is  brain dead. This is a state of healing and regeneration and can also be found by deep meditation.

How Do Sleep Apps Work?

You can understand your own sleep better by using free sleep apps. One of our favorites is Sleep Cycle, which can do several things.

The alarm clock function will give you the option of waking up at a specific time or to be woken up in 30 minutes, where you're in the lightest phase of sleep (stage 1 or 2). Almost everyone wakes up with an alarm clock with no thought or planning as to the best time to be woken up. Your chosen wake up time may be when you're in REM or deep sleep, which is difficult to wake from, and if you are woken up in these stages, you'll feel groggy.

The app will also track and graph your phases of sleep. You can see below what time you fell asleep, how long you slept, how many sleep cycles you went through, and when you went through them.

sleep cycle app

Every night you have to record how well you slept and when you woke up, so you can start to make connections with what is making you sleep better and worse. You can also add your own sleep notes, such as "exercised," "drank coffee," or "stressful day" to see what could be influencing your sleep quality.

The app works by tracking your movement either through the microphone or the accelerometer, which can graph where you're at in your sleep cycle by how much you're moving. The app will also record your snoring!

What Is a Sleep Study?

Sleep studies are prescribed for people who are having issues getting to sleep, staying asleep, or waking up feeling unrested. It's normal for everyone to have an occasional bad night of sleep, but if someone regularly has sleep issues, their doctor will probably refer them to a sleep clinic who will administer the study.

Sleep studies normally occur in a sleep clinic where you sleep in a room that will look somewhat like a hotel. It's non-invasive, and you will be connected to electrodes that will track your brain activity while other sensors track your heart rate, eye movements, snoring, and oxygen levels in the blood. There are no needles involved.

This information is recorded by the sleep tech and then is shared with your doctor who will analyze the results.

References And Continued Reading