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Understanding the Stages of Sleep

Learn why deep sleep and REM sleep are so important to a healthy life.

Sleep is the way that your body restores itself, recharging so that you feel refreshed and active when you wake up. Getting enough high-quality sleep is an important part of a lifestyle that enables physical, emotional, and mental health. Without enough sleep, you may notice decreased work performance, mood instability, and a lack of energy. Over time, with enough sleep deprivation, lack of sleep can cause larger health issues like diabetes, heart disease, and obesity.[1] Learning about the stages of sleep, and what happens in each of them, can help you develop a healthier sleep cycle that allows you to be the best version of yourself.

The Four Stages of Sleep

When you sleep, your body enters different phases of sleep, sometimes referred to as “sleep architecture.”[2] While researchers used to break it down into five stages of sleep, many sleep experts now combine two of the stages into one state. Most literature now uses a sleep classification system that includes four distinct stages of sleep during the sleep cycle.[3] Throughout a full night of sleep, people typically experience four to six full sleep cycles.[4]

There are two basic types of sleep: rapid eye movement (REM) sleep and non-REM sleep.[5] The first three stages of sleep are non-REM (NREM), and the final stage is REM.

Stage 1 NREM: This stage is the “dozing off” period, typically lasting less than five minutes. Activity in the body and brain start to slow down, including a slower breathing pattern and occasional muscle twitches.[6] It’s easy to be woken up from this stage, but if left undisturbed, a person will quickly slip into the next stage of sleep.

Stage 2 NREM: The next stage of NREM is a period of light sleep lasting anywhere from 10 minutes to an hour. The muscles in the body relax even further, body temperature drops, and eye movements stop. Throughout the night, the body usually spends most of its time in Stage 2 sleep.[7]

Stage 3 NREM: This is the period of deep sleep (sometimes called “slow-wave sleep”) that your body depends on to feel refreshed in the morning.[8] This typically lasts between 20 and 40 minutes. Heartbeat and breathing patterns slow to their lowest levels, and it’s difficult to wake up during this phase.

Stage 4 REM: This is the final stage of the sleep cycle: REM sleep. Brain waves become more active during this phase and eyes move erratically underneath the lids. Dreaming usually happens in this state. As you age, you tend to spend less time in this stage of the sleep cycle.

Why REM Sleep is So Important

Your body needs deep sleep in order to reap the necessary, restorative benefits of sleep. When it comes to REM sleep in particular, some sleep experts believe that REM sleep is essential for cognitive functions like memory and learning.[9] A recent study also suggests that REM sleep might help with processing stress or trauma while also providing additional mental resilience against difficult experiences.[10] Another study from Berkeley found similar results, noting that during REM sleep, the chemical associated with stress decreases drastically, allowing the mind to process traumatic events and wake up with a lower emotional response to triggers—sort of like an unconscious therapy session.[11] [12] And while causation hasn’t been confirmed, poor-quality REM sleep has been associated with Alzheimer’s disease.[13]

What Interferes with REM Sleep?

If your sleep cycle and REM sleep is disrupted, it can not only be jarring or frustrating but it can prevent your body from resting and recharging as much as it needs to. Understanding the triggers for worsened sleep quality or interrupted sleep can help you avoid them and get a more restful night of sleep.

  • Alcohol. While drinking can make it easier to fall asleep, it makes it harder for the body to sink into the deeper stages of the sleep cycle, and often leads to a more disruptive night of sleep.[14]
  • Caffeine. Stimulants such as caffeine can increase activity in the brain and cause insomnia, or an inability to fall asleep. Coffee, tea, or even over-the-counter drugs like decongestants can sometimes contain high levels of caffeine that may disrupt your ability to experience REM sleep.[15]
  • Very hot or cold temperatures. During REM sleep, the body is less able to regulate body temperature. Experiencing extreme temperatures can cause the body to wake up prematurely.[16]
  • Obstructive sleep apnea or other sleep disorders. Sleep apnea can cause breathing to stop, which disrupts the sleep cycle and can restrict sleep to stages 1 and 2—reducing the opportunity for high-quality deep sleep.[17] Investing in

Developing a Healthier Sleep Cycle

It’s important to prioritize a sleep schedule that will provide you with ample, quality sleep so that your body can heal and rejuvenate. Focusing on improving the factors that will enable a good sleep cycle. This will pay dividends for your health and wellness. Make sure to find your ideal sleep and wake schedule that allows you to get the right amount of sleep. If you find yourself struggling with insomnia or another sleep disorder that is preventing you from enjoying a consistent sleep cycle, it’s best to check in with a medical professional. Deep sleep is an important part of maintaining your physical, emotional, and mental health, and focusing on your sleep is one critical aspect of taking care of your well-being.



[3] PubMed






[9] Harvard Med

[10] Journal of Neuroscience


[12] Time

[13] Science Direct

[14] Cleveland Clinic

[15] PubMed

[16] Cleveland Clinic