Medically reviewed by Brandy Hall, MSN, RN, 02/01/2023
REM, or rapid eye movement, is the crucial last phase of each sleep cycle. It earned its easy acronym for the side-to-side movement our eyes make during this stage. Luckily our lids are closed, or we might look a little creepy. But the movement has a specific purpose. REM is the sleep stage in which we dream, and that eponymous eye movement is how we watch what unfolds in our dreams, whether it’s a wonderful travel getaway or the recurring end-of-semester test-taking nightmare that happens even years after you’ve left school.
To understand REM, it helps to first understand sleep cycles. A good night of sleep is made up of four to six sleep cycles, each lasting 90 to 110 minutes. Each cycle contains four phases. The first three phases are known as non-REM, so they are labeled NREM1, NREM2, and NREM3. Then, we finally slip into REM, which is the state in which we most commonly dream — hopefully about winning the lottery.
What happens during REM sleep?
REM comes after NREM3, which is a deep sleep in which your body and brain go into repair mode, and your heart rate and breathing rate both slow considerably. REM, as the final phase of a sleep cycle, helps you prepare for waking or the start of your next sleep cycle — think of it as a buffer period. During REM, your heart rate and breathing rate will increase again after having been much slower in NREM3.
As the name suggests, your eyes rapidly move during REM. But why do they get so shifty? It’s because they’re scanning your dream imagery. Sleep scientists had long suspected this was the case, and a 2015 study published in Nature Communications confirmed it. Each dart of the eyes correlates with a new dream image, almost as if your brain is clicking through a slideshow or scrolling through your phone’s camera roll.
Although your eyes are moving, the rest of your body is still. That’s because your muscles are paralyzed to protect you from acting out your dreams. The neurotransmitters gamma-aminobutyric acid (GABA) and glycine depress the parts of your brain that impact muscle movement. This loss of muscle movement likely serves as a safety mechanism, keeping you comfy on your mattress rather than acting out the dreams your darting eyes are seeing. People who have REM sleep behavioral disorder lack this muscle paralysis during REM and may flail their limbs, yell, or otherwise move around while asleep. However, we all occasionally may have an episode of acting out our dreams, especially if we’ve had a stressful day.
During REM, your brain is also doing a lot of work. For one thing, REM helps with your memory. During NREM3, your hippocampus fires up new information gleaned from your day and trains your cortex for storage. Then during REM, researchers believe the brain consolidates and stabilizes those newly stored memories. Think of REM as doing a little organizing in the bookshelf of your mind.
REM also works its magic on our procedural memory. We all have those things we can do almost as if we were on autopilot, whether that’s playing a specific piano piece or making a latte. At one point, these things were new to you, just like learning to ride a bike or drive a car. We build a new skill through repetition, and REM helps us stamp that training into our memory. Think about that dance routine you learned when you were 10 that you still somehow know. REM did some of that work for you.
How much REM sleep do you need?
About 25% of your sleep is spent in REM. How much REM sleep you need will depend on how much sleep you require in general to feel rested. As a rule of thumb, adults should aim for seven to nine hours of sleep per night. Within this window, you’ll log 105 to 135 minutes of REM sleep.
If you set an alarm and wake up feeling super tired, you may need to boost your sleep time so that you can gain more REM. While a little fogginess upon waking is normal, waking up extra foggy could mean you’re being jolted out of NREM3 (the deep-sleep phase) and experiencing what’s called sleep inertia.
Ideally, you’ll wake up gradually from REM sleep, which researchers theorize is meant to help us transition out of deeper sleep. The good news: As your sleep sessions progress over the course of the night, you’ll spend more time in each REM phase and less time in NREM3.
What happens if you don’t get REM sleep?
If you don’t get enough REM for one or two nights because of shortened sleep sessions, you may feel groggy from not having had enough sleep cycles. Over time, you could feel more forgetful, too.
Longer-term deficits in REM sleep, however, are associated with health concerns, including an increased risk of all-cause mortality (death from any cause) and cardiovascular and non-cancer-related deaths. That sounds bleak, but the study authors point out that their research does not conclude that less REM sleep leads to a higher risk of death, only that the two things are associated — possibly other factors are at play.
Ultimately, more research is needed to understand any health concerns from not getting enough REM sleep. But we do know that REM is an important part of sleep cycles, and adequate sleep is imperative for your immune system to function at its best, so it’s a good idea to get enough sleep.
How long should REM sleep last?
When you first go to sleep, you’ll reach the REM phase roughly 90 minutes into your first sleep cycle and spend about 10 minutes in that first REM phase. The phase is short — and hopefully includes a sweet dream.
Then with each subsequent sleep cycle, you’ll spend less time in the deep sleep of NREM3 and spend more time in lighter NREM2 and REM. Your final REM phase may even last 60 minutes, all ultimately adding up to that 105 to 135 minutes of total REM sleep per night. Use our sleep calculator to ensure you’re getting enough sleep, according to the time you need to wake up.
How to support healthy REM sleep
Allowing for plenty of time to sleep is one of the best ways to ensure you’re getting enough REM sleep. But there are a few additional ways to support healthy sleep cycles and the REM phase.
- Limit caffeine to earlier in your day. Caffeine throughout the day is associated with a delay in REM sleep, according to a 2021 study. This may limit how much you ultimately get.
- Skip that late-night cocktail too close to bedtime. Alcohol initially might help you fall asleep, but it may slow your progression to REM sleep and affect the quality and quantity of REM sleep.
- Some prescription medications can also affect REM sleep. If you think a medication is impacting your slumber, talk to your health care provider about your symptoms. They may be able to prescribe an alternative.
- Some conditions, such as sleep apnea and insomnia, can also lead to less REM sleep. If you suspect you have a sleep disorder, talk to your health care provider. Treatment may be able to help you improve sleep architecture and get more REM sleep.
In general, if you aim to get enough sleep time, you should log enough REM time. Doing so will help you feel revitalized rather than worn-out when waking. And may the dreams your rapidly moving eyes see always be good ones.
