Sleep Disorders The 4 Stages of Sleep What happens in the brain and body during NREM and REM sleep By Kendra Cherry Kendra Cherry Facebook Twitter Kendra Cherry, MS, is an author, educational consultant, and speaker focused on helping students learn about psychology. Learn about our editorial process Updated on October 02, 2022 Medically reviewed by Daniel Combs, MD Medically reviewed by Daniel Combs, MD Daniel Combs, MD, is board-certified in sleep medicine and pediatrics. Learn about our Medical Expert Board Print Table of Contents View All Table of Contents Falling Asleep NREM Stage 1 NREM Stage 2 NREM Stage 3 Stage 4: REM Sleep Sequence of Sleep Stages Cycle Interruptions Impact of Poor Sleep Frequently Asked Questions As you sleep, your brain cycles through four stages of sleep. The first three are considered non-rapid eye movement (NREM) sleep, also known as quiet sleep. The fourth is rapid eye movement (REM) sleep, also known as active sleep. In stage 1, you transition from wakefulness to sleep. In stage 2 you enter light sleep. By stage 3 you are in a deep sleep. Stage 4 REM, known as paradoxical sleep, is when the body's immobilized and dreams occur. Each sleep stage has a unique function and role in maintaining your brain's overall cognitive performance. Some stages are also associated with physical repairs that keep you healthy and get you ready for the next day. The entire sleep cycle repeats itself several times a night, with every successive REM stage increasing in duration and depth of sleep. This article discusses the four stages of sleep. It also explains what happens during each sleep stage and what can hinder your sleep. Verywell / JR Bee Falling Sleep Using an electroencephalogram (EEG), a non-invasive test that records brain activity, scientists are able to see how the brain engages in various mental activities as a person falls and is asleep. During the earliest phases of sleep, you are still relatively awake and alert. At this time, the brain produces what are known as beta waves—small and fast brainwaves that mean the brain is active and engaged. As the brain begins to relax and slow down, it lights up with alpha waves. During this transition into deep sleep, you may experience strange and vivid sensations, known as hypnagogic hallucinations. Common examples of this phenomenon include the sensation of falling or of hearing someone call your name. There's also the myoclonic jerk; if you have ever been startled suddenly for seemingly no reason at all, then you have experienced this. Aren't There 5 Stages of Sleep? Sleep used to be divided into five different stages, but this was changed by the American Academy of Sleep Medicine (AASM) in 2007. NREM Stage 1 The first stage of the sleep cycle is a transition period between wakefulness and sleep. If you awaken someone during this stage, they might report that they were not really asleep. During stage 1 sleep: Your brain slows downYour heartbeat, your eye movements, and your breathing slow with itYour body relaxes, and your muscles may twitch This brief period of sleep lasts for around five to 10 minutes. At this time, the brain is still fairly active and producing high amplitude theta waves, which are slow brainwaves occurring mostly in the brain's frontal lobe. NREM Stage 2 According to the American Sleep Foundation, people spend approximately 50% of their total sleep time during NREM stage 2, which lasts for about 20 minutes per cycle. During stage 2 sleep: You become less aware of your surroundingsYour body temperature dropsYour eye movements stopYour breathing and heart rate become more regular The brain also begins to produce bursts of rapid, rhythmic brain wave activity, which are known as sleep spindles. They are thought to be a feature of memory consolidation—when your brain gathers, processes, and filters new memories you acquired the previous day. While this is occurring, your body slows down in preparation for NREM stage 3 sleep and REM sleep—the deep sleep stages when the brain and body repair, restore, and reset for the coming day. NREM Stage 3 Deep, slow brain waves known as delta waves begin to emerge during NREM stage 3 sleep—a stage that is also referred to as delta sleep. This is a period of deep sleep where any noises or activity in the environment may fail to wake the sleeping person. Getting enough NREM stage 3 sleep allows you to feel refreshed the next day. During NREM stage 3 sleep: Your muscles are completely relaxedYour blood pressure drops, and breathing slowsYou progress into your deepest sleep During this deep sleep stage, your body starts its physical repairs. Meanwhile, your brain consolidates declarative memories—for example, general knowledge, facts or statistics, personal experiences, and other things you have learned. Stage 4: REM Sleep While your brain is aroused with mental activities during REM sleep, the fourth stage of sleep, your voluntary muscles become immobilized. During REM sleep, your brain's activity most closely resembles its activity during waking hours. However, your body is temporarily paralyzed—a good thing, as it prevents you from acting out your dreams. REM sleep begins approximately 90 minutes after falling asleep. At this time: Your brain lights up with activityYour body is relaxed and immobilizedYour breathing is faster and irregularYour eyes move rapidlyYou dream Like stage 3, memory consolidation also happens during REM sleep. However, it is thought that REM sleep is when emotions and emotional memories are processed and stored. Your brain also uses this time to cement information into memory, making it an important stage for learning. Repair Work in Progress During deep sleep (stage 3 and REM), your cells repair and rebuild, and hormones are secreted to promote bone and muscle growth. Your body also uses deep sleep to strengthen your immunity so you can fight off illness and infection. Dreaming Sleep and Sleep Cycles Sequence of Sleep Stages It's important to realize that sleep does not progress through the four stages in perfect sequence. When you have a full night of uninterrupted sleep, the stages progress as follows: Sleep begins with NREM stage 1 sleep.NREM stage 1 progresses into NREM stage 2.NREM stage 2 is followed by NREM stage 3.NREM stage 2 is then repeated.Finally, you are in REM sleep. Once REM sleep is over, the body usually returns to NREM stage 2 before beginning the cycle all over again. Time spent in each stage changes throughout the night as the cycle repeats (about four to five times total). Sleep architecture refers to the exact cycles and stages a person experiences in a night. A sleep specialist may show you this information on what's known as a hypnogram—a graph produced by an EEG. How Long Is a Sleep Cycle? A full sleep cycle is generally around 90 to 110 minutes long. What Can Interrupt Your Cycle Any time you have trouble falling asleep or staying asleep at night, your sleep cycle will be affected. Interrupted sleep is the term used to describe sleep that is not continuous throughout the night. When this happens, your sleep cycle can be disrupted. An in-progress sleep stage may be cut short and a cycle may repeat before finishing. There are a number of issues that can interrupt your sleep cycles. Depending on which one is at play, this may happen occasionally or on a chronic basis. Some factors that are associated with interrupted sleep and, therefore, may affect your sleep stages include: Older age: Sleep naturally becomes lighter, and you are more easily awoken. Nocturia: Frequently waking up with the need to urinate Sleep disorders, including obstructive sleep apnea (breathing that stops and starts during sleep) and restless leg syndrome (a strong sensation of needing to move the legs) Pain: Difficulty falling or staying asleep due to acute or chronic pain conditions, like fibromyalgia Mood disorders such as depression and bipolar disorder Other health conditions including Alzheimer's disease, Parkinson's disease, obesity, heart disease, and asthma Lifestyle habits: Little/no exercise, cigarette smoking, excessive caffeine intake, excessive alcohol use What Happens When Sleep Stages Are Altered Not spending enough time in each sleep stage or properly cycling through the stages of sleep can affect you in a variety of ways, having potentially short-term and long-term consequences. A few examples of issues that can arise from a disrupted sleep cycle include problems with: Learning and focusingBeing creativeMaking rational decisionsSolving problemsRecalling memories or informationControlling your emotions or behaviors People with a disrupted sleep cycle are also at greater risk for: PainInflammationHigh blood pressureHeart diseaseOverweight/obesityDiabetesReduced quality of life Summary As your body progresses through the four stages of the sleep cycle—stages 1 through 3 (non-rapid eye movement, or NREM) and stage 4 (rapid eye movement, or REM), it transitions through different biological processes that affect your temperature, breathing, cells, and muscles. All the while, your brain is busy forming, organizing, and storing memories. The sleep cycle follows a specific pattern, but that can be interrupted because of variety of habits, health conditions, and even older age. Over time, not getting enough sleep and not cycling through the four stages can cause physical and mental health issues. A Word From Verywell It's important not just to get seven to nine hours of sleep per night, but to ensure it's uninterrupted, quality sleep that allows your body to benefit from each of these four stages. If you experience any of the following, make an appointment to see your healthcare provider, as you may not be getting the sleep you need: You are having trouble falling or staying asleep at least three nights per weekYou regularly wake up feeling unrestedYour daytime activities are affected by fatigue or mental alertnessYou often need to take a nap to get through the dayA sleep partner has told you that you snore or gasp when you are asleepLack of sleep is affecting your mental wellbeing Frequently Asked Questions How long is each sleep stage? NREM stage 1: Less than 10 minutes, begins right after falling asleepNREM stage 2: Lasts anywhere from 30 to 60 minutesNREM stage 3: Lasts between 20 to 40 minutesREM sleep: About 10 minutes for the first period during sleep, then increasingly longer with later periods Is REM the deepest sleep? Yes, REM is the deepest phase of sleep. Each sleep stage gets progressively deeper, with NREM stage 3 and REM the deep-sleep phases. How much REM sleep do you need? There isn't a specific recommendation for how much REM sleep is needed. This is due to REM taking place in multiple intervals for varying lengths of time. However, most adults should try to get a total of at least seven to nine hours of sleep total each night. How do I increase my REM sleep? There is no cut-and-dried approach to increasing REM sleep. However, the longer you sleep, the more REM you get. Sticking to a regular sleep schedule and keeping your room cool and dark can help. Learn More: Tips for Better, Longer Sleep Can you live without REM sleep? Yes, but it is rare. People who have a sleep disorder like insomnia may experience limited REM sleep. This causes a condition known as dream deprivation. Learn More: What Is Dream Deprivation? Can REM sleep cause nightmares? Nightmares occur during REM sleep, but REM sleep does not cause them. Nightmares are more common during the latter half of your sleep when REM cycles are longer. Learn More: Why You Have Nightmares During what sleep cycle does sleep walking occur? Sleepwalking typically occurs during NREM stage 3 sleep. It is more common in the early part of your night's sleep. Children and young adults are more likely to sleepwalk than older adults. Learn More: Why Do People Sleepwalk? 10 Ways to Get a Better Night of Sleep 19 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. National Institute of Neurological Disorders and Stroke. Brain basics: understanding sleep. Vijayan S, Lepage KQ, Kopell NJ, Cash SS. Frontal beta-theta network during REM sleep. Elife. 2017 Jan;6(1):1-19. doi:10.7554/eLife.18894 Moser D, Anderer P, Gruber G, et al. Sleep classification according to AASM and Rechtschaffen & Kales: Effects on sleep scoring parameters. Sleep. 2009;32(2):139-149. doi:10.1093/sleep/32.2.139 Sleep Foundation. Stages of sleep. Andrillon T, Nir Y, Staba R. Sleep spindles in humans: Insights from intracranial EEG and unit recordings. J Neurosci. 2011 Dec;31(49):17821-17834. doi:10.1523/JNEUROSCI.2604-11.2011 Sleep Foundation. What happens when you sleep?. Feld G, Diekelmann S. Sleep smart—optimizing sleep for declarative learning and memory. Front Psychol. 2015 May;6(1):622. doi:10.3389/fpsyg.2015.00622 Glosemeyer R, Diekelmann S, Cassel W, et al. Selective suppression of rapid eye movement sleep increases next-day negative affect and amygdala responses to social exclusion. Sci Rep. 2020 Oct;10(1):17325. doi:10.1038/s41598-020-74169-8 Johns Hopkins Medicine. The Science of Sleep: Understanding What Happens When You Sleep. Cleveland Clinic. Sleep basics. Sleep Foundation. Interrupted sleep. Centers for Disease Control and Prevention. Short sleep duration among US adults. Medic G, Wille M, Hemels ME. Short- and long-term health consequences of sleep disruption. Nat Sci Sleep. 2017 May 19;9:151-161. doi:10.2147/NSS.S134864 Sleep Foundation. How much sleep do we really need?. University of Michigan Health. Stages of sleep. National Institute of Neurological Disorders and Stroke. Brain basics: Understanding sleep. National Library of Medicine: MedlinePlus. Healthy sleep. Scarpelli S, Bartolacci C, D'Atri A, Gorgoni M, De Gennaro L. Mental sleep activity and disturbing dreams in the lifespan. Int J Environ Res Public Health. 2019;16(19):3658. doi:10.3390/ijerph16193658 National Library of Medicine: MedlinePlus. Sleepwalking. By Kendra Cherry Kendra Cherry, MS, is an author, educational consultant, and speaker focused on helping students learn about psychology. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit