Sleep - A Complete Guide To REM Sleep and Sleep Stages

Sleep - A Complete Guide To REM Sleep and Sleep Stages

As many as 70 million Americans have a sleep disorder, with over one-third of young adults (20-39 years old) sleeping less than 7 hours per night. [1,9]

What’s more, we actually take pride in our ability to shirk off sleep, saying such crass things as “I’ll sleep when I’m dead.”

Why do we treat sleep so disparagingly?

Probably because we’re an arrogant species that think we’re smarter than we actually are. You see, humans have evolved over 3.8 million years and sleep has been a vital part of that evolution.

Related - 25 Tips to Help You Get a Better Night's Sleep

Why else do you think we spend one-third of our natural lives in this passive state?

Because sleep is absolutely essential to living a healthy life, and this goes far beyond building muscle or burning fat.

Sleep is the time when the body does the majority of its maintenance work, repairing the damage from the previous day and building us anew so that we can tackle the new challenges awaiting us.

So, what happens when we don’t get enough sleep?

The Consequences of Sleep Deprivation

If you’re one of those individuals who so casually casts aside sleep, you might be thinking, “what’s the worst that could happen? I’ll just be a little more tired than usual and need a bit more coffee (and/or pre-workout) to get through the day.”

And while all of that is true, being a bit more tired is just the beginning of your problems.

Quite simply, when we are sleep deprived, we’re more vulnerable to a laundry list of things, including:


  • Impaired memory and learning
  • Inability to sustain attention
  • Downregulation of dopamine D2 and D3 receptor availability (which messes with the reward-motivation system in the brain)
  • Diabetes
  • Obesity
  • Anxiety
  • Depression
  • Stroke
  • Heart attack
  • Cancer
  • Alzheimer’s disease


Brain regions and networks associated with attention and working memory (frontoparietal network (FPN); red), arousal (thalamus; green) and the default mode network (DMN; blue) are affected by sleep deprivation. [2]

Also worth noting is the fact that men who only sleep 5-6 hours per night have testosterone levels similar to that of a man 10 years their senior!

Furthermore, subtle changes also occur in regards to our negative emotional processing, where we end up more emotionally volatile, irritable, anxious, and aggressive. [3,4,5,7]

Studies have also shown that when animals are deprived of REM Sleep, cardiac dysfunction ensues. [13]

Perhaps most disturbingly, suicidal ideation, suicide attempts and suicide completion are all increased following periods of sleep deprivation, too! [6]

Hopefully by now, at the very least, you are convinced of the importance of sleep. But, if not, let’s delve a little deeper into the various aspects of sleep to see what happens when you’re knocked out at night.

The Science of Sleep

Sleep is far more complex than you might imagine. Sure, your physical body is relatively motionless, but there is a cascade of activity going on within your mind and body.

Every sleep cycle is divided into two distinct parts:

  • Rapid eye movement (REM) sleep and
  • Non-rapid eye movement sleep (Non-REM Sleep).

More on Non-REM Sleep

Non-rapid eye movement sleep can be further divided into four stages called stages 1, 2, 3, and 4 (yes, it’s very imaginative…)

Stage 1

Stage 1 (light sleep) occurs within minutes of falling asleep and lasts only about seven minutes or so. During this phase, the brain produces alpha and theta waves and your eye movements slow down.

Stage 2

During stage 2, which is also fairly light sleep, the brain produces sudden increases in sleep spindles which are oscillations that look like an EEG brain activity. Researchers believe this oscillatory action is key to sensory processing and long term memory consolidation. [8]

Note, if you’re a fan of “power naps”, this is the stage you want to wake up after, as your brain has had time to make connections and store the info you were trying to learn and memorize.

Stage 3 & Stage 4 (“Deep Sleep”)

Stages 3 and 4 of non-REM sleep are referred to as deep stages of sleep where by the body does a lot of its upkeep and repairs, especially on the cardiovascular system and brain.

During deep sleep, the brain generates slower delta waves, and it becomes more difficult to be awakened because your body is less responsive to external stimuli.

With each passing sleep cycle, the brain produces more delta waves, driving you deeper and deeper into sleep.

As you might expect, muscle activity (including eye movement) is virtually nill at this point as the body is doing major repairs to all the various muscles and tissues. During this phase, growth and development occur and immune function gets some much needed TLC too. You can essentially think of Stage 3 and Stage 4 sleep as your own mini “fountain of youth.”

How “productive” and successful we are at achieving these deep stages of sleep ultimately determines how well we perform the next day as well as how well we fend of illness and disease.

Predator Alert?!

Interestingly, half of your brain does not enter into those two deep stages of sleep when you’re sleeping in a strange environment (i.e. spending the night in a hotel while on vacation or a business trip).

This also is probably why we never really feel completely “refreshed” from a night’s rest until we’re back home in our own comfy, cozy beds.

Sleep researchers theorize this is an evolutionary mechanism that had its roots in threat detection.

You see, millennia ago when man was roaming the wilderness in a loincloth, climbing trees for fruit, and spearing anything he came across for food, he didn’t have a quaint red brick house and white picket fence to retire to at the end of a long day.

He slept in a cave, under a tree, or anywhere that seemed relatively safe and didn’t leave him wide open to attack from a bloodthirsty lion or fellow man seeking to plunder, pilfer, and pillage.

In this somewhat dubious state, half the brain remains alert in “threat detection” mode ready to kick you out of your slumber at a moment’s notice and hopefully save you from getting kidnapped, stabbed, or eaten.

Note, these are also the stages of sleep most people miss out on the most, which is part of the reason we always feel so run down and overworked.

Now that we’ve covered Non-REM sleep, let’s check out the other major component to our nightly repose -- REM sleep.

More on REM Sleep

REM sleep is also known as dream sleep, quite simply because it is when we are in REM sleep that we dream. We spend approximately 25% of the night in REM sleep, and it occurs 90 minutes after we fall asleep and repeats every 90 minutes after that.

During REM sleep the brain is highly active, and our eyes are darting back and forth. Breathing also becomes faster and irregular, and our heart rate and blood pressure rise to levels similar to that of when we are awake.

Yet, our bodies are essentially motionless and relaxed as the muscles are inactive during this phase.

Why is REM sleep important?

REM sleep is important for supporting daytime performance and increasing energy reserves that will be consumed by both the mind and body the ensuing day.

It’s also needed for emotional and mental health, and REM sleep stimulates regions of the brain regions used in learning. REM sleep even involves the increased production of proteins in the body.

And, if you’re still not quite convinced of why REM sleep is important, then consider this:

Animal studies from the 1980s show that when deprived of REM sleep, the rats die as quickly as if they had been deprived of food! [11,12]

Defending Mind and Body

We’ve mentioned several times throughout this article that the brain enacts various repair and growth mechanisms while we sleep. And it even helps bolster the immune system.

But, emerging research indicates it may be an important line of defense in protecting against cognitive decline.

Cerebrospinal fluid is a clear liquid that surrounds the brain and spinal cord. It washes across the brain using a series of channels that surround blood vessels. The network through which this fluid circulates is called the glymphatic system, and it is managed glial cells -- non-neuronal cells that surround neurons where they provide support and insulation for them.

Researchers have found that the glymphatic system can help remove a toxic protein called beta-amyloid from the brain. [15]

Why is this important?

Well, beta-amyloid is one of the leading candidates behind memory impairment associated with Alzheimer’s disease and aging. [14]

And, researchers have found a pretty clear link between β-amyloid pathology with impaired Non-REM sleep.

In other words, if you want to increase your chances for preserving your memory and staving off cognitive decline as you age...GET YOUR SLEEP!

Quality Is Just as Important as Quantity

Some of the emerging research in sleep science is in regards to both quality and quantity being important. For years now, we’ve all been told to get 7-9 hours of sleep, but not much was said in regards to how good (quality) that sleep needed to be.

What this means, is that even if you’re getting 7-9 hours of sleep each night, but those hours are spent tossing and turning, never entering into the deep stage 3 and stage 4 sleep, you’re not really recovering as well as you could...which bears more consequences than just feeling a bit groggy as we detailed at the outset of this article.

How Sleep Changes with Age

We’ve all heard the expression, “sleep like a baby.” It usually refers to sleeping so deeply and soundly that an earthquake could happen and you’d be none the wiser.

Unfortunately, as we age, our ability to enter this coma-esque type sleep fades.

In fact, with each passing decade, our sleep changes fairly drastically. [17]

  • We tend to go to bed earlier and awaken earlier
  • It takes us longer to fall asleep
  • We sleep a shorter amount of time
  • We experience increasing bouts of wakefulness and arousal during the night
  • Our sleep is more “fragile” (more easily woken up)
  • We spend more time in “light sleep” (non-REM stages 1 & 2)
  • We spend less time in “deep slow wave sleep” (non-REM stages 3 & 4)
  • We have fewer sleep cycles every night

Basically, the deck is stacked against us the older we get, which makes doing anything and everything we can to ensure a proper night’s sleep absolutely critical.

Along those lines...

The Effects of Alcohol & Marijuana on Sleep

We all tend to have stressful days from time to time, and in our efforts to cut loose and shirk of the bothersome toils of the day, we tend to unwind by indulging in a nightcap or possibly smoking marijuana.

And, while both of these may help take the edge off (alcohol is a depressant and sedative after all), they both impair REM sleep, but by different mechanisms.

Essentially, what happens is that alcohol knocks out the cortex temporarily putting you into a state of sedation, which is different than natural sleep. Alcohol also impacts sleep in another way -- it leads to more periods of wakefulness during the night such that you won’t feel fully restored the next morning.

Now, here’s the interesting thing, most people aren’t aware of these increased number of awakenings during the night, so they go on having their nightcaps and happy hours all the while thinking it’s improving their sleep when in reality it’s actually running them down further.

The brain keeps track of how much dream sleep you should be having. The less dream sleep you get, the “hungrier” it becomes for dream sleep.

So, when your body finally clears the alcohol from its system, the brain gets what it wants and causes something called “REM sleep rebound” whereby you get the normal amount of REM sleep that you should normally get, plus some of the dream sleep that you’ve been missing the past few days, weeks, and months. [16]

When these REM sleep rebounds occur, it’s not uncommon to have very intense, vivid dreams.

For example, let’s use the typical Friday night bender the average person takes every week to celebrate the end of another work week. 5 PM hits, and they hit up a local happy hour and while away the next several hours drinking, joking, and cajoling.

When it’s closing time, they head home and fall straight into bed. All this time, alcohol is still swirling through their body and the brain cannot enter into REM sleep. Some five to six hours into your repose, the last of the alcohol is excreted from the kidneys and liver and your brain can finally get what it’s been craving all night -- dream (REM) sleep.

Suffice it to say, the next few hours will be crazier than Mr. Toad’s Wild Ride from a dream vividness perspective.

In alcoholics, they have something called delirium tremens (DT) which is the rapid onset of confusion usually caused by withdrawal from alcohol.

Alcohol has been blocking their ability to sleep for so long that when the alcohol is finally removed from their system the brain’s thirst for dream sleep is so vicious and intense, it spills over into the person’s wakefulness.

Essentially, you start to dream while you are awake (delirium)!

Hopefully, by now you’re starting to grasp the concept of just how important sleep is to the brain. It will force you to dream even while you’re awake in order for it to get what it wants. Talk about a tyrannical entity!

How Can We Get Better Sleep?

Sleep is crucial to living a long, healthy, and enjoyable life. The days of casting aside sleep to “live it up” needs to be tempered, and we need to start placing as great of an emphasis on sleep as we doing eating right and training hard.

That being said, what can we do to sleep better at night?

  • Maintain a regular sleep schedule (e.g. go to bed and wake up at the same time, even on weekends)
  • Make your room as dark as possible
  • Keep your room cool 65-68 degrees Fahrenheit (your brain needs to drop its temperature by 2-3 degrees in order to fall asleep)
  • Avoid blue light exposure 2 hours before going to bed
  • Limit stressful events during the day and avoid them at all costs in the immediate hours before bed (checking email, social media, angry phone calls with in-laws, etc.)
  • Limit caffeine intake during the day and try to end your caffeine intake 6-8 hours before bed
  • Do what you love for a living (we spend more time at work than we do at home. If you hate your job, that stress will continue to compound and ruin your ability to sleep soundly)
  • Avoid alcohol and marijuana in the hours before bed
  • Take a warm bath at night (when you get out of the tub, core temperature drops as your body tries to dissipate heat, allowing you to be cooler and sleep better)

1) "Sleep Statistics - Data About Sleep and Sleep Disorders." American Sleep Association, 22 Aug. 2016,

2) Krause AJ, Simon EB, Mander BA, et al. The sleep-deprived human brain. Nat Rev Neurosci. 2017;18(7):404–418. doi:10.1038/nrn.2017.55

3) Anderson C, Platten CR. Sleep deprivation lowers inhibition and enhances impulsivity to negative stimuli. Behav Brain Res. 2011;217:463–466

4) Horne JA. Sleep function, with particular reference to sleep deprivation. Ann Clin Res. 1985;17:199–208.

5) Dinges DF, et al. Cumulative sleepiness, mood disturbance, and psychomotor vigilance performance decrements during a week of sleep restricted to 4–5 hours per night. Sleep. 1997;20:267–277.

6) Bernert RA, Joiner TE. Sleep disturbances and suicide risk: A review of the literature. Neuropsychiatr Dis Treat. 2007;3(6):735–743. doi:10.2147/ndt.s1248

7) Minkel JD, et al. Sleep deprivation and stressors: evidence for elevated negative affect in response to mild stressors when sleep deprived. Emotion. 2012;12:1015–1020.

8) De Gennaro, L., & Ferrara, M. (2003). Sleep spindles: an overview. Sleep Medicine Reviews, 7(5), 423–440.

9) Institute of Medicine. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington, DC: The National Academies Press; 2006.

10) "Brain Basics: Understanding Sleep." National Institute of Neurological Disorders and Stroke | National Institute of Neurological Disorders and Stroke, 8 Feb. 2019,

11) Kushida, C. A., Bergmann, B. M., & Rechtschaffen, A. (1989). Sleep deprivation in the rat: IV. Paradoxical sleep deprivation. Sleep, 12(1), 22–30.

12) Rechtschaffen, A., Bergmann, B. M., Everson, C. A., Kushida, C. A., & Gilliland, M. A. (1989). Sleep Deprivation in the Rat : X . Integration and Discussion of the Findings, 12(August 1988), 68–87.

13) Giampá, S. Q. de C., Mônico-Neto, M., de Mello, M. T., Souza, H. de S., Tufik, S., Lee, K. S., Antunes, H. K. M. (2016). Paradoxical Sleep Deprivation Causes Cardiac Dysfunction and the Impairment Is Attenuated by Resistance Training. PLOS ONE, 11(11), e0167029.

14) Mander BA, Marks SM, Vogel JW, et al. β-amyloid disrupts human NREM slow waves and related hippocampus-dependent memory consolidation. Nat Neurosci. 2015;18(7):1051–1057. doi:10.1038/nn.4035

15) Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373–377. doi:10.1126/science.1241224

16) Tore Nielsen, Philippe Stenstrom, Tomoka Takeuchi, Sebastien Saucier, Jessica Lara-Carrasco, Elizaveta Solomonova, Emilie Martel, Partial REM-Sleep Deprivation Increases the Dream-Like Quality of Mentation From REM Sleep and Sleep Onset, Sleep, Volume 28, Issue 9, September 2005, Pages 1083–1089,

17) Mander BA, Winer JR, Walker MP. Sleep and Human Aging. Neuron. 2017;94(1):19–36. doi:10.1016/j.neuron.2017.02.004

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