Stages of the Sleep Cycle: What Happens During Light, Deep, and REM Sleep

You’re doing everything right on paper. The bedroom is dark, the phone is charging in another room, and you’re even trying that expensive pillow everyone raves about. Yet, somehow, you’re still dragging yourself through the day wondering why sleep feels so elusive.

That’s because getting enough hours in bed and getting quality sleep is completely different. Research shows that only 15% of people manage to get adequate sleep for at least five days a week, according to Sleep Health, regardless of how long they stay in bed.

That’s because the problem isn’t always how long you sleep. It’s how well you sleep. Your brain follows a specific pattern of the four stages of the sleep cycle, each serving a unique purpose. Knowing what these are is the first step to enjoying mornings where you feel well-rested and refreshed?

What Is the Sleep Cycle?

Your brain doesn’t just shut off when you go to sleep. Instead, it cycles through different types of sleep stages, each serving a unique purpose in restoring your body and mind. Sleep researchers have found two main categories: rapid eye movement (REM) sleep and non-rapid eye movement (NREM or non-REM) sleep, which breaks down into three specific phases, according to the National Library of Medicine. 

Most people cycle through these stages four or five times on a typical night, with each complete cycle lasting around 96 minutes, according to Sleep Health. Each stage has its own role, from light dozing to the deepest stages for restoration where your body repairs itself. Missing out on any of these stages can leave you feeling groggy or unfocused the next day.

Stage 1: N1 - Light Sleep

N1 is your gentle introduction to sleep, where you’re not quite awake but not fully asleep either. Your brain waves start to slow down from their wakeful patterns, and your muscles begin to relax. You might experience those sudden jerking movements that sometimes startle you awake during this phase.

This is when your body starts its nightly restoration work. Your heart rate starts to slow, and your breathing becomes more regular. While you’re not getting the deep recovery benefits yet, N1 sleep gives your nervous system permission to start winding down from the day’s activities.

Even though N1 is the lightest sleep stage, it’s still extremely important for brain function. This is when your brain starts shifting gears from processing external stimuli to focusing inward. Your mind starts to let go of the day’s worries and distractions as you settle in for deeper sleep.

Stage 2: N2 - Deeper Light Sleep

N2 sleep takes relaxation to the next level. Your brain waves continue to slow down with some brief bursts of activity called sleep spindles and K-complexes, which are natural brain patterns that help protect your sleep time from external stimuli. 

Your body temperature drops even more, and your blood pressure continues to plummet. At this point, your muscles relax completely, and your breathing becomes even more regular and steady. While you’re still relatively easy to wake up during N2, your brain is working to consolidate the lighter memories and experiences from your day to decide what to keep and what to let go.

Stage 3: N3 - Deep Sleep

Deep sleep is where the magic happens. Your brain produces its slowest waves of the night, and your body becomes almost completely still. This is the hardest stage to wake up from, and you’ll feel groggy and disoriented if someone wakes you during N3 sleep. That’s because your brain goes into maintenance mode as it clears out toxins.

Your body uses this stage to get to work on repairing itself. Growth hormone surges through your system to rebuild tissues and restore energy for the next day. Your bones and muscles get their most intensive repair work done during these deep sleep periods.

All this work makes this stage extremely important for overall health. A study found that the adults who got the most deep sleep had a 70% lower risk of developing diabetes compared to those who got the least of it, according toThe Journal of Clinical Endocrinology & Metabolism.

Stage 4: REM Sleep

REM sleep is a form of active sleep when your brain becomes almost as busy as when you’re awake, but your body enters a state of temporary paralysis that prevents you from acting out your dreams. Your eyes dart back and forth very quickly (hence the name!) while your brain goes to work. This fascinating stage starts about an hour after you fall asleep and gets longer with each cycle throughout the night. That’s why many people use white noise for sleep, as it helps prevent these disruptions from waking you up. 

This stage helps you process the emotional experiences of your day, reducing their intensity and helping you wake up feeling more emotionally balanced. People who get adequate REM sleep can handle stress better and have more stable moods. Your brain also uses this time to strengthen neural connections related to learning and creativity, which explains why you sometimes wake up with solutions to problems that stumped you the day before.

It’s also incredibly important for long-term brain health. People who regularly fail to get enough REM sleep are muchmore likely to develop dementia, as each percentage point decrease in REM sleep increases the risk of developing dementia by almost 10%, according to a sleep study published in Neurology. That shows that prioritizing your sleep does a whole lot more than help with beauty.

What Affects Sleep Stages?

Your sleep cycle is surprisingly fragile. Even small disruptions can throw off the delicate balance between stages, causing daytime sleepiness despite spending enough time in bed. There are so many obstacles that can keep you from resting well, like the blue glow of your phone or the stress of tomorrow’s deadline. These are some of the biggest sleep hygiene issues that can disrupt your sleep:

• Stress and anxiety: Your mind struggles to transition into deep sleep when it’s busy processing worries about work or daily life. This mental activity triggers elevated stress hormones like cortisol, which keep your brain alert when it should be winding down. The effects compound over time because chronic stress makes falling asleep harder while simultaneously reducing the amount of sleep you spend in the most restorative stages.
   
• Exposure to blue light: The screens on your devices emit blue light that tricks your brain into thinking it’s still daytime. This disruption suppresses melatonin production, which is the hormone that tells your body it’s time to sleep.
   
• Inconsistent sleep schedule: Going to bed and waking up at different times confuses your internal clock. Your body thrives on routine, and these irregular sleep patterns prevent your circadian rhythm from establishing the predictable cycles you need for quality rest. Without this consistency, your brain never knows when to start preparing for sleep.
   
• Caffeine and alcohol: Caffeine can stay in your system for up to eight hours, blocking the brain chemicals that promote sleepiness. Alcohol is also a problem because, even though it might help you fall asleep faster, it disrupts your sleep cycles later in the night. Even just two drinks with dinner can have a negative effect on your time in REM sleep, according to Sleep Medicine Reviews.
   
• Environmental factors: Temperature, noise, and light in your bedroom all impact how well you cycle through sleep stages. A room that’s too warm can keep you from reaching deep sleep, while unexpected sounds can fragment your cycles throughout the night.
   
• Sleep disorders: Conditions like obstructive sleep apnea can reduce your time asleep and prevent you from completing a full REM cycle. People with sleep apnea can experience breathing interruptions that disrupt how much sleep they get per night and mess up their REM stages.

How to Improve Your Sleep Cycle

Most people complete four to six full cycles of sleep stages each night when everything goes according to plan. You need light sleep for the transition, deep sleep for physical restoration, and REM sleep for emotional and cognitive processing. Every stage has a purpose, so it’s important to shoot for good scores across the board.

Improving your sleep cycle starts with consistency and the right tools to track your progress. Wellhub is a comprehensive wellness platform that gives you access to many of these tools:

• Sleep Cycle: This app helps you understand exactly how much time you spend in each stage and wakes you during lighter sleep phases so you feel more refreshed.
   
• Rise Science: This app works with your natural circadian rhythms to time your daily activities for better sleep.
   
• Headspace: This platform provides hundreds of guided meditations for sleep designed to calm your mind and make it easier to transition into deep hours of sleep.

Better Sleep Cycles Can Support a Healthier Mind and Body

Sleep is so much more complex than just closing your eyes for eight hours of sleep per night. As you rest, your brain cycles through all four stages of the sleep cycle to give your body the deep restoration it needs. 

But knowing what good sleep looks like and how to achieve it are two different things. Stress, inconsistent schedules, blue light, and environmental factors can disrupt your natural cycles. That’s where having the right support makes all the difference.

You might already have access to Wellhub through your employee benefits. Check here to see if you’re eligible and start exploring sleep-tracking tools and meditation apps. If not, start a petition to bring Wellhub to your company.

References: 

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• Bonsignore, M. R., Mazzuca, E., Baiamonte, P., Bouckaert, B., Verbeke, W., & Pevernagie, D. A. (2024). REM sleep obstructive sleep apnoea. European Respiratory Review, 33(171). https://doi.org/10.1183/16000617.0166-2023
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