What is REM Sleep and Why is It Important?

Athletic couple in deep REM sleep in bed together
Sleep has experienced a renaissance of sorts the past few years after being callously cast aside as “optional” by significant portions of the population for decades. Whereas it was commonplace to hear the phrases "I'll sleep when I'm dead" or "sleep is for babies and old people," these days more and more individuals recognize the essentiality of sleep and not only make time for it but prioritize it just like their workouts and diet plans. This “sleep renaissance” is in large part due to the engrossing work of high-profile sleep researchers, such as Dr. Mathew Walker. Today, we’re covering all things sleep -- REM sleep, non-REM sleep, sleep stages, and much more. Let's start by discussing a straightforward topic:

Why Do We Sleep?

We spend ⅓ of our lives sleeping (or at least, we’re supposed to). As such, sleep is not only important, but it is essential. Animal studies have found that total sleep deprivation results in death within two or three weeks. <4> These studies can't be replicated in humans, but research has found that even as little as 24 hours of sleep deprivation can lead to hallucinations and other symptoms associated with schizophrenia. <5> For these reasons (and many others), the Guinness Book of World Records has done away with tracking how long an individual can stay awake and go without sleep. If for no other reason, understand that we need to sleep at a basic level to survive. But, that’s not all as you’re about to see. For a long time, researchers had no idea why we needed to sleep or what happened at a physiological level. All we knew was that we needed to do it. Fortunately, over the past couple of decades, sleep researchers have begun to gain a better understanding of the events that transpire during our nightly repose. For starters, sleep is needed to solidify and consolidate memories. <1,2> Every day, our minds are bombarded by vasts amount of information -- some of it is useful/pertinent, but the vast majority isn't (e.g., 99% of the things shown on social media). As we receive these various data feeds, our brains temporarily store the information in our cerebral cortex. You can think of it as the RAM of a computer -- a place with limited storage capacity that allows for quick retrieval of recently acquired information. Our brains need to encode the information we've learned and associated it with memories or facts we've learned and encoded it in our long-term memory which is located in the hippocampus. Continuing the computer analogy, the hippocampus is similar to the hard drive of your computer. It has considerably more space and is best for storing things long term. This process of learning, information connection, memory consolidation, and storage occurs while we sleep. In other words, if you're not getting enough sleep, you're hurting your mind's ability to process, learn, and encode the information you've learned. For example, sleep researchers have found that people tend to retain information and perform better on memory tasks after they sleep. <3> Beyond memory consolidation and learning, sleep is also required to:
  • Synthesize Hormones
  • Build and Repair Muscle Tissue
  • Restore and Rejuvenate Energy Levels
Now, that we’ve gotten a better understanding of why we need to sleep, let’s dive a little deeper into the different stages of sleep our bodies go through each night.

What are the Different Stages of Sleep?

Sleep is divided into two distinct states: REM (rapid eye movement) sleep and non-REM sleep. When you first drift off to sleep, your body goes into the lighter stages of non-REM sleep, which progresses into deeper stages, ultimately moving into REM sleep. This entire cycle lasts between 90-110 minutes and is repeated several times throughout the night. Let’s now to a closer look at the various stages of non-REM and REM sleep.

Non-REM Sleep

Stage 1

Stage 1 is the lightest stage of sleep. We enter into it upon falling asleep, and it lasts only a brief amount of time (less than 10 minutes). Since stage 1, sleep is so light, it's very easy to be awakened during it. Moreover, during stage 1 sleep, you are aware of your surroundings but will become more and more relaxed as you drift deeper into sleep. It’s also not out of the ordinary to have strange, illogical thoughts during this time, or the whole-body twitches where you feel like your falling. Finally, eye movement starts to slow, and core body temperature drops as you drift off.

Stage 2

Stage 2 is another lighter stage of sleep. One in which you can easily be awakened. During stage 2 sleep, heart rate and blood pressure decrease, eye movements cease, and the upper airway relaxes. It's also possible to have fragmented dreams during this part of the sleep cycle. Stage 2 sleep makes up the majority of our sleep each night as it accounts for between 45–50% of total sleep time in healthy young adults. That means if you’re getting the recommended 8 hours of sleep, 3.5–4 hours of that sleep is spent in stage 2.

Stage 3 and Stage 4 (Deep Sleep)

Depending on which classification system you’re looking at, deep sleep is comprised of either one or two stages (Stage 3 and Stage 4). You may also hear this phase of the sleep cycle referred to as slow-wave sleep (SWS). This is the most restorative and rejuvenating stage of sleep and could be considered as the most important sleep stage concerning cognitive health. The reason for this is during deep sleep the glymphatic system removes waste products from the brain, such as neurotoxins and beta-amyloids. Other necessary actions that take place during deep sleep include growth hormone release, cell repair and rejuvenation, glycogen replenishment, and long-term memory formation and information storage. Similar to stage 2 sleep, deep sleep is characterized by decreased heart rate and blood pressure as well as no eye movements. Additionally, body temperature continues to drop, and muscle activity decreases. And, it's also worth mentioning that night terror, sleepwalking, sleep talking, and confusion arousals may also occur during deep sleep. <6> Deep sleep typically lasts 20-40 minutes, and it is the most difficult part of the sleep cycle to wake a person. Should you be awakened (or wake someone else up) during this stage, expect to feel a fair bit groggy or disoriented. Deep sleep concludes the non-REM part of the sleep cycle. After moving through the three (or four) stages of non-REM sleep, the next part of the sleep cycle is REM Sleep.

What is REM Sleep?

REM stands for rapid-eye-movement sleep, and it is the portion of sleep when the body is motionless while the brain is highly active. As the name implies, during REM sleep, it’s quite common for the eyes to dart side-to-side, though this movement doesn’t occur the entire time we are in REM sleep. Compared to earlier non-REM stages of sleep, heart rate and blood pressure increase slightly during REM sleep, and breathing becomes shorter. Additionally, body temperature falls to its lowest point of the night during REM sleep. Our initial foray into REM sleep typically lasts for 10 minutes; however, each time we enter REM sleep during the night the duration gets progressively longer such that our final trip through REM sleep can last for up to an hour! As we mentioned, the brain is highly active in REM sleep, but the body is in a state of temporary paralysis which is caused by signals from the brain that stop the movement of the arms and legs. Researchers theorize that this lack of muscle activity (known as atonia), may be a protective mechanism of sorts to prevent us from injuring ourselves (or anyone else that happens to be sleeping next to us) as a result of us acting out our dreams. <7>

Five Fast Facts About REM Sleep

  • REM sleep occupies approximately 25% of the total sleep time.
  • Newborns spend up to 80% of their time asleep in REM sleep.
  • During REM sleep, our breathing can become fast and irregular.
  • Late evening or nighttime consumption of alcohol can impair the quantity of REM sleep.
  • The brain is almost as active during REM sleep as it is when we are awake.

REM Sleep vs. Non-REM Sleep

We've covered a lot of ground thus far, and at this point, it might be prudent to help recap and summarize the differences between the two main phases of sleep -- non-REM and REM sleep. So…

Body Movement

During non-REM sleep, the body is lightly active (twitches and such), but during REM sleep, the body is in a state of temporary paralysis.

Eye Movement

REM sleep gets its name from the fact that the eyes dart back and forth during this phase. However, during non-REM sleep, eye movement is absent.


Light, fractured dreams can occur during non-REM sleep, but our most vivid dreams occur during REM sleep.

Sleep Ratio

We spend the majority of our time sleeping in stage 2, which accounts for between 45-50% of total sleep time. REM sleep accounts for approximately 20–25% of total sleep time, which means you spend roughly 1.5-2 hours in REM sleep per night.

How to Improve REM Sleep

As a whole, society struggles to get enough sleep due to a myriad of issues. Given the importance that sleep plays in helping you perform to your best, both mentally and physically, here is a list of things you can do to improve the quality and duration of your sleep each night.

Establish a Routine

We are creatures of habit. We tend to wake up at the same time, eat around the same times each day, work out the same time each day, and go to the office the same time each day. Why should sleep be any different? It is an essential part of our day that cannot be ignored. As such, one of the best things you can do to help get your body ready for sleep is to go to bed at the same time each night. But more than that, establish a nighttime routine in the 90-120 minutes before you want to fall asleep. Doing so helps signal to your mind and body that it’s time to wind down for the day and prepare to rest.

Avoid Alcohol at Night

We said it earlier, but we'll repeat it. While alcohol may decrease the amount of time it takes you to fall asleep (a characteristic is known as sleep latency), consuming it late at night disrupts REM sleep and can reduce the number of REM sleep stages you experience. If at all possible, avoid alcohol in the hours immediately preceding sleep.

Limit Blue Light Exposure

This tip goes part and parcel with our first suggestion of establishing a nighttime routine. Blue light is a short wavelength, high energy color on the visible light spectrum, which has both benefits and drawbacks. Due to its intensity, blue light is excellent for helping us wake up and be alert -- this is why it is recommended that we get exposure to outdoor light as soon as we can in the morning. However, come nighttime, blue light is the enemy as exposure to it impairs melatonin production. Melatonin is the hormone the regulates our circadian rhythm and sleep-wake cycle. Constant bombardment from blue light by laptops, LED lights, TVs, tablets, and smartphones throws off the natural production of melatonin in the evenings, thereby impairing our ability to fall asleep when we’d like to. Blue blocker glasses can help as can turning down the brightness on your devices (or using apps which “dampens” the amount of blue light on the screen). An even better option would be to avoid any and all screen 1-2 hours before bed and use dim lighting.

Avoid Napping Too Late

Naps can be great to help give you a boost in energy during the day after a night of poor sleep. There’s also some evidence that a short power nap can help improve learning and memory too. <8> However, napping for too long or too late in the day can disrupt your ability to get to sleep at your regularly scheduled time. As such, if you want to nap, try to get it in sometime around mid-day and make sure it doesn’t last too long (> 1 hour).

Limit Caffeine Intake

Caffeine is a stimulant and wakefulness-promoting compound. It works primarily by antagonizing adenosine receptors in the body. Adenosine is a neurotransmitter in the brain that induces sedation and relaxation. When you consume caffeine, it binds to the adenosine receptors in the brain, inhibiting adenosine from doing its job, and the result is increased feelings of alertness, energy, and focus. Therefore, you are trying to get to sleep; it's a good idea to avoid caffeine in the hours leading up to sleep. Moreover, caffeine has a half-life of 5-6 hours, which means that after 5 hours have elapsed 50% of the caffeine that you ingested is still in your blood. So, if you take a pre-workout supplement that contains 300mg of caffeine at 4 PM for your after-work workout, come 10 PM when you're trying to go to sleep, you still have ~150mg of caffeine coursing through your body. If you're particularly sensitive to caffeine, this is the perfect prescription for a night of tossing, turning, and poor sleep. In general, it's recommended that you cut-off your caffeine intake by 3 PM each day so as not to overly disrupt sleep. If you're extremely sensitive to the stimulatory effects of caffeine, consider cutting off your caffeine intake by noon.

Keep Your Room Cool

Being comfortable is essential to falling asleep and staying that way. Sleep researchers recommending keeping your room temperature between 60- and 67-degrees Fahrenheit to promote better sleep.

Consider a Sleep Supplement

Sleep supplement is a dual-edged sword. Some help you relax and unwind while others knock you out cold, leave you feeling groggy, and impair REM sleep. We created Steel Dreams® to be your all-natural nighttime recovery and relaxation aid. Steel Dreams® contains only natural ingredients (such as L-theanine and KSM-66) that are non-habit forming and will not lead to feelings of grogginess or impair sleep quality.

Why is REM Sleep Important?

Sleep is an essential part of everyday life. Why else do you think we’ve evolved to spend ⅓ of our entire life doing it?! If you wake up feeling refreshed and invigorated, then keep doing what you’ve been doing. However, if you find that you’re waking up groggy, irritable, or “foggy” and/or relying on copious quantities of caffeine to get you through your day, then use the tips in the article to help get better sleep and be on your way to a happier, healthier, more productive life.


  1. Rasch B, Born J. About sleep's role in memory. Physiol Rev. 2013;93(2):681–766. doi:10.1152/physrev.00032.2012
  2. Klinzing, J. G., Niethard, N., & Born, J. (2019). Mechanisms of systems memory consolidation during sleep. Nature Neuroscience.
  3. Gais, S., Lucas, B., & Born, J. (2006). Sleep after learning aids memory recall. Learning & Memory (Cold Spring Harbor, N.Y.), 13(3), 259–262.
  4. Rechtschaffen, A., & Bergmann, B. M. (1995). BEHAVIOURAL Sleep deprivation in the rat by the disk-over-water method, 69, 55–63.
  5. Petrovsky, N., Ettinger, U., Hill, A., Frenzel, L., Meyhöfer, I., Wagner, M., … Kumari, V. (2014). Sleep Deprivation Disrupts Prepulse Inhibition and Induces Psychosis-Like Symptoms in Healthy Humans. The Journal of Neuroscience, 34(27), 9134 LP – 9140.
  6. Shrivastava D, Jung S, Saadat M, Sirohi R, Crewson K. How to interpret the results of a sleep study. J Community Hosp Intern Med Perspect. 2014;4(5):24983. Published 2014 Nov 25. doi:10.3402/jchimp.v4.24983
  7. "Brain Basics: Understanding Sleep." National Institute of Neurological Disorders and Stroke | National Institute of Neurological Disorders and Stroke.
  8. Li, J., Cacchione, P. Z., Hodgson, N., Riegel, B., Keenan, B. T., Scharf, M. T., … Gooneratne, N. S. (2017). Afternoon Napping and Cognition in Chinese Older Adults: Findings from the China Health and Retirement Longitudinal Study Baseline Assessment. Journal of the American Geriatrics Society, 65(2), 373–380.

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