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"Ever noticed how everything feels harder to process after a bad night’s sleep? That’s your brain struggling without enough REM"
You've probably heard of the phrase REM (rapid eye movement.) But you might be less clear on the crucial role this sleep stage has on our overall health and wellbeing.
During each night, our sleep consists of four to six cycles, which are each broken down into three stages of NREM (non-rapid eye movement) sleep and finally, one stage of REM sleep.
The term REM was coined by researchers in the 1950s to describe the movements our eyes make while we're in this stage of sleep, which is now understood to be when our most vivid dreaming occurs.
And while REM sleep is, in part, characterized by dreams, there's so much more to it. Did you know that, according to research, it's when our brains are most active during sleep, and that we typically wake up in the morning during the middle of this sleep stage?
And that it helps with everything from memory to processing emotions, immunity and the development of our brains?
For Sleep Awareness Week 2025 we’re going to explore more of the research and speak to experts about what it is, why it’s so important for our brains and bodies, how much we really need and how we can ensure we get it. Read on for everything you need to know about REM sleep…
What is REM sleep?
"REM sleep is the final stage of the sleep cycle where the brain becomes highly active, almost as if it’s awake, while the body remains relaxed. This is the stage where vivid dreams happen," says certified sleep consultant and founder of The Sleep Works, Maryanne Taylor.
The last of the four sleep stages, it is characterized (and named) by the fact that your eyes are quickly moving behind your eyelids.
While the first three stages of sleep, N1, N2 and N3 is when our sleep transitions from lightest to deepest, REM sleep is the phase of sleep we dream the most, when our brains process emotions, form and consolidate certain types of memories, and much more.
This sleep stage also, according to UCI Health, has the restorative effect of allowing us to feel alert and refreshed when we wake up.
However, apart from this movement of the eyes and of muscles that help us breathe, our bodies are otherwise paralyzed, according to the National Institute of Health, so that we can’t physically act out what is occurring in our dreams.
As the researchers explain, “the skeletal muscles are atonic and without movement, except for the eyes and diaphragmatic muscles, which remain active."
We actually spend around 25% of our sleep in the REM stage as adults, and researchers describe the beta brain waves that are recorded during this time as “similar to brain waves during wakefulness.”
Added to that, our breathing, blood pressure and heart rate increase, according to Harvard Health.
When does REM sleep occur?
According to UCI Health, a healthy 7 to 9 hours of sleep should include a total of between 1 hour 45 minutes and 2 hours 15 minutes of REM sleep. But when exactly are we in this sleep stage?
"REM sleep happens in the final stage of our sleep cycle, following light and deep stages," says Taylor.
"The first periods of REM sleep are shorter, but they lengthen as the night progresses. Most of our REM sleep occurs during the second half of the night," Taylor adds.
Each sleep cycle typically lasts 90 to 110 minutes, with REM sleep being the final stage, per the National Institute of Health. While the first bout of REM sleep might only last 10 minutes, you'll eventually end up having as much as an hour of REM sleep in your later sleep cycles.
What does REM sleep do?
1. Helps process emotions
"Researchers believe that REM sleep plays a role in memory processing and dealing with emotions," says Dr. Lindsay Browning, neuroscientist, sleep expert and psychologist at Trouble Sleeping.
She explains that it's the vivid dreams that occur in this stage of sleep and what we're dreaming that may be able to help us work through challenging experiences and feelings:
"Dream topics may include potential future situations (such as dreams about turning up for an exam when you haven’t revised), or reflect unresolved emotional issues, or could be seemingly random," Dr Browning says.
"In post-traumatic stress disorder, for example, people tend to have repeated nightmares about the trauma which is the brain’s way of trying to understand what has happened," she adds.
Plus, research has shown that the amygdala is particularly active during REM sleep.
"REM sleep helps regulate the amygdala, the part of your brain that controls emotions," says says UKCP-registered psychotherapist specialising in sleep and author of How to Be Awake (So You Can Sleep Through the Night), Heather Darwall-Smith, citing research from 2014.
"Without it, stress hormones (like cortisol) stay high, making you feel more anxious, overwhelmed, or emotionally reactive," she adds. "It’s like walking around with an emotional magnifying glass, making everything seem bigger and worse than it really is."
2. Helps consolidate memory
Our brains are more active during REM sleep — higher frequency beta waves that we experience during this stage are similar to those we have when awake, alert and processing information.
As such, REM sleep is significant for memory since while in it you "process and consolidate new information you've learned," Harvard Health says.
However, it's generally understood to be non-REM sleep (light and deep sleep) that is vital to memory consolidation, and, Dr Browning explains, there is less clarity on the exact role of REM sleep.
"One theory is that non-REM sleep is used for memorising facts, while REM sleep may have a role in processing skill based and emotional memories (especially as there is increased activity in the area of the brain associated with emotions, the amygdala, during REM sleep)," she says.
There is research that says REM sleep plays an important part in processing and consolidating emotional memory.
Another study on rats showed increased REM sleep improved their memories when it came to performing certain recently learned tasks, while decreasing REM sleep seemed to "primarily impair memory formation on complex tasks."
3. Aids brain development
Many studies have indicated that REM sleep is important in the development of the brain. One reasons that scientists believe this is the fact that babies spend much longer in REM sleep than adults do.
In fact, recent research into infants, sleep and the brain noted that, "the greater time spent sleeping in infancy and early childhood is thought to reflect the crucial role sleep (especially REM sleep) plays in fostering optimal brain development, cognition, and behavior."
Even as we get older, REM sleep remains important. It supports neuroplasticity – the brain’s ability to adapt, reorganise, and keep learning throughout life.
"Newborns spend up to 50% of their sleep in REM because their brains are growing rapidly," Darwall- Smith says, citing research from 2008.
"During this stage, the brain strengthens connections between nerve cells – helping with learning, emotional regulation, and cognitive development," she adds.
"Even as we get older, REM sleep remains important. It supports neuroplasticity – the brain’s ability to adapt, reorganise, and keep learning throughout life."
Dr. William Lu, Dreem Health medical director and sleep medicine physician with a primary specialty in family medicine, explains that REM sleep is also involved in a 'pruning' of the brain's synapses.
"REM sleep helps facilitate the process of “synaptic pruning” where the brain selectively strengthens important neural connections while eliminating unnecessary ones, effectively refining and optimizing neural pathways established during learning and experiences throughout the day."
4. Improves learning
If you're trying to learn a new skill and want the best chance of mastering it, then REM sleep is your friend.
"REM sleep aids learning by actively processing and consolidating new information required during the day," says Dr. Lu.
"Essentially, REM sleep strengthens memories by reinforcing important neural connections while turning away unnecessary ones," he adds.
Darwall-Smith says that REM sleep works hand-in-hand with N3 stage deep sleep to help with learning and memory, and that both are vital for this process.
REM sleep is key in linking ideas, problem-solving, and refining skills
"[Deep sleep] helps store facts and knowledge, while REM sleep is key in linking ideas, problem-solving, and refining skills," she explains. "Studies using polysomnography (a type of sleep study) show that when people don’t get enough REM sleep, they struggle with memory tasks and learn less efficiently."
"Researchers found that REM sleep is needed for procedural memory – the type of memory that helps you learn motor skills (like playing an instrument or riding a bike)," Darwall-Smith continues.
"When REM sleep was disrupted, people performed worse on tasks requiring coordination and practice."
5. Boosts immunity
Sleep plays a vital role in keeping us healthy, and one aspect of REM sleep is that it helps with boosting our immunity. It's a complex process that involves both N3 deep sleep and REM sleep, but the experts have given us some insight into what's actually happening.
"During REM sleep, the body produces and regulates crucial immune system cells and cytokines during its active brain wave state," says Dr. Lu. Cytokines are "signaling proteins that help control inflammation in your body," according to the Cleveland Clinic.
"Cytokines and immune system cells are primarily produced during deep sleep," he adds. "However REM is still very important in the immune system process as you get more sympathetic nervous system (active state) activity and subsequent NF-kB activity which helps to activate inflammatory processes.
"There are cellular levers being pulled between nonREM and REM states all the time during sleep," he says.
"Deep sleep builds your immune system, and REM sleep regulates and fine-tunes it," says Darwall-Smith agrees. During deep sleep growth hormones are released to build cells and repair tissues, and cytokines are produced for fighting infection and helping the body's response to vaccines, she says.
REM sleep then "fine-tunes them, making sure your immune system doesn’t overreact or underreact," Darwall-Smith explains, adding that this assists in controlling inflammation and helps regulate cortisol levels.
6. Dreaming
While we do dream during other sleep stages, it's widely accepted that the bulk of it happens during REM sleep, and in particular the most vivid dreams we experience.
We know this because, as researchers explained in a 2001 edition of Neuroscience, subjects awoken during REM sleep reported "elaborate, vivid, hallucinogenic and emotional dreams," where as those who were woken up during other stages of sleep reported less dreaming, and those that did had dreams which were less intense and emotional.
The fact that, as we mentioned above, the amount of REM sleep we experience increases over the period of time we're asleep, means that more of your vivid dreaming is likely to occur in the latter part of the night.
How much REM sleep do we need?
"Adults should get 20 to 25% of their sleep in REM sleep, averaging to about 1.5 to 2 hours if they sleep 7 to 9 hours a night," says Dr. Lu (a similar amount to the 1 hour 45 minutes and 2 hours 15 minutes noted by UCI Health).
However, the amount of REM sleep we need and get does depend on age. Darwall-Smith outlines how this changes through our lifetimes:
Newborns: 50% of total sleep is REM.
Children and adolescents: 20-25% of total sleep (around 2 hours per night).
Adults: 20-25% of total sleep.
Older adults: Slightly less REM sleep, but still around 20%.
What happens if you don’t get enough REM sleep?
Ensuring you get enough sleep overall is, of course, the best way to ensure a healthy body and mind. But if you lack in REM sleep in particular, there can be specific consequences to your wellbeing.
"Insufficient REM sleep can lead to cognitive impairment, emotional disturbances, and in more severe cases can lead to a weakened immune system, increased risk of cardiovascular disease, high blood pressure, and metabolic disorders," Dr. Wu says.
Ever noticed how everything feels harder to process after a bad night’s sleep? That’s your brain struggling without enough REM
Darwall-Smith adds: "Not getting enough REM sleep makes remembering things, solving problems, and regulating emotions harder (Walker, 2009). Ever noticed how everything feels harder to process after a bad night’s sleep? That’s your brain struggling without enough REM."
She notes that as well as causing issues with emotional regulation, "long-term REM sleep deprivation is linked to Alzheimer’s and Parkinson’s because it stops the brain from clearing out toxic proteins that build up over time. Consistently missing REM sleep doesn’t just affect how you feel now – it affects brain health in the long run."
How to get more REM sleep
It's not possible (yet!) to control exactly how long we spend in the REM sleep stage, or any sleep stage for that matter. However, certain lifestyle factors can influence REM sleep and sleep overall, which we'll explore below...
Keep a regular sleep schedule
"As REM sleep happens more in the later part of the night, it is important to improve sleep patterns overall," says Taylor, adding that "keeping consistent with sleep times as much as possible," is important for regulating sleep cycles.
That means aiming for the same bedtime each night, even on weekends, and ideally the same wake up time too.
Avoid caffeine and alcohol
"Limit alcohol close to bedtime," says Taylor, "as it can disrupt sleep cycles and interfere with quality of REM sleep."
Having a few drinks with dinner or while out in the evening is typical of many. But alcohol has been shown to have a negative impact on REM sleep. One study showed that larger amounts of alcohol delays the onset of this stage of sleep, while others referenced in the same research indicated that moderate to high doses can also lead to an overall decrease in REM sleep.
Caffeine also has a disruptive effect on our sleep, particularly if consumed close to bedtime. Ideally cut off your intake of caffeine 6 to 8 hours before you head to sleep, as chemicals such as melatonin promote sleep, but caffeine can block them.
Manage stress and anxiety
Stress can lead to higher levels of cortisol (the hormone that makes us feel awake and alert) which can disrupt your sleep. Anxiety, meanwhile, can also increase cortisol levels and result in the likes of panic attacks and worry — which aren't great for getting to sleep and staying asleep.
A review of research looking into the effects of stress on sleep has also shown that experimental stress and psychosocial stressors can reduce REM sleep, while major life stressors can increase REM sleep, and decrease slow wave sleep (none of these impacts are great for your overall wellbeing, since we need to effectively cycle through all sleep stages to feel refreshed).
If you want to create the best chance overall of getting a good rest, Taylor says that it's important to wind down before sleeping, explaining that "calming, relaxing activities before getting into bed helps signal to your brain it is time to sleep."
That could be creating a relaxing nighttime routine, perhaps with meditation, a soothing bath, stretching, reading or listening to calming music. However, if your sleep is regularly disrupted by stress and anxiety it's important to speak to your doctor.
Tom's Guide created this content as part of a paid partnership with Helix Sleep. The contents of this article are independent and solely reflect the editorial opinion of Tom's Guide.
