What Are the Stages of Sleep?

How Sleep Works

Your sleep schedule and regulation are determined by two processes: your homeostatic sleep drive and your circadian rhythm.

Your homeostatic sleep drive is your body’s natural inclination to want sleep after you’ve been awake for a certain period of time. For most people, this drive is fairly easy to predict. The longer you’re awake, the higher your sleep drive gets. Once you’ve given your body and brain the rest it needs, your sleep drive is reset, and you’re back to normal wakefulness.

Your brain also regulates sleep through your circadian rhythm, also known as your sleep-wake cycle. This is your body’s natural clock, and it sets itself based on several environmental factors, namely light. This is why we get tired at night and are alert during the day.

The Four Sleep Cycle Stages

When you go to sleep, you’ll go through four stages. Each stage does something different to your body and your brain. These four stages—each lasting about 90 minutes—will cycle throughout the night until you wake up for the day. 

These sleep stages can be categorized as awake, light sleep, deep sleep, and rapid eye movement (REM) sleep. Each stage is important and is necessary to make you feel healthy and restful the next day. Each stage of sleep is also categorized as a non-rapid eye movement state (NREM) or a REM state. The first three phases of sleep are considered NREM, while the final stage of sleep is REM.

1. Awake

The first stage of sleep is the awake stage. This NREM stage is the lightest stage of sleep. Your awake state is when you’re lying in bed at night and when you’re lying in bed in the morning before waking up. This stage can also include any periods of awakening you have throughout the night. In the first stage, you slow your heart and breathing, you relax your muscles, and your brain begins to ready itself for sleep.

2. Light Sleep

The next stage is light sleep, which is another NREM stage of sleep. As you enter this deeper part of the sleep cycle, your muscles continue to relax, and your heartbeat continues to slow. Your breathing rate slows down, and brain activity continues to change. In this stage, your body temperature will also begin to drop. 

During this stage of the sleep cycle, you’re sensitive to changes in noise, touch, temperature and light. It’s easier to wake up out of this stage of sleep as compared to deeper sleep. 

Dreaming can occur in this stage of NREM sleep, but these dreams are shorter and simpler in comparison to the more vivid dreams that happen during REM sleep.

3. Deep Sleep

The third stage of sleep, deep sleep, is an NREM stage. Deep sleep is when your body and brain really repair themselves. Your heartbeat and breathing will be at their slowest, and your body will be at its most relaxed. During deep sleep, you’re less likely to wake up from environmental noise or light. If you do wake up, you’ll likely feel more groggy or disorientated.

Deep sleep allows your body to grow and repair muscle. Your brain activity will also exhibit long, slow waves and flush waste out.

4. REM Sleep

Finally, the last stage of the sleep cycle is the REM stage. This stage is marked by your eyes moving rapidly beneath your eyelids, thus the rapid eye movement moniker. REM sleep is when your respiration speeds up and your heart rate increases. In addition, your muscles may be immobile to prevent your body from reacting to dreams, which primarily occur during REM sleep. REM sleep can also re-energize your mind.

NREM vs. REM Sleep

NREM and REM sleep are two very different phases of the sleep cycle, but each phase has its own benefits.

Non-REM sleep makes up the vast majority of the sleep cycle—three out of the four stages. Two of these NREM stages are when you get your deepest sleep. It can be more difficult to wake up from NREM sleep. While you’re in NREM sleep, your body can build bone and muscle, repair tissue, and build a stronger immune system. NREM sleep decreases as you get older, with older adults getting the least amount of deep sleep.

REM sleep will typically start about an hour to an hour and a half into your sleep cycle. During REM sleep, you can have vivid dreams. Your brain activity increases so much during this stage that it is similar to your waking levels of activity. Your first REM stage will be relatively short, with each period of REM getting longer throughout your sleep cycle.

What Is the Purpose of Sleep Cycles?

Sleep cycles are essential to having a healthy body and mind. They also help you feel refreshed and rested when you wake up. 

Here are just a few of the changes your body experiences while you’re going through your sleep cycle:

• Regulating your hormones: Healthy sleep can help to regulate your hormone levels.
• Maintain your weight: Regulating hormones also helps to regulate your metabolism and your appetite. Getting enough sleep can help you maintain a healthy weight and decrease your risk for obesity.
• Muscle recovery and growth: Your body uses the deep sleep cycle to repair and regenerate tissues, repair muscle fibers, and build bone strength. This is especially important if you exercise regularly or if you’ve been injured recently.
• Strengthen the immune system: Sleep allows your immune system to recover and build strength to fight infections and lower your risk for other health issues. 
• Healthy heart: When you sleep, your heart rate and blood pressure gradually decrease to levels that aren’t possible while you’re awake. This can help decrease your risk for high blood pressure and other heart-related issues.
• Skin repair: Good sleep can help your skin regenerate and look brighter and healthier.

What Does a Normal Sleep Cycle Look Like?

A normal sleep cycle will vary based on the individual. Everyone has slightly different sleep needs depending on their age, activity, and other factors. However, there is a general baseline of how much sleep you should be getting. 

You want to be able to go through the stages of sleep around four to five times per night. For most people, a full cycle takes around 90 minutes. The cycle will usually go in the order we talked about earlier: awake, light sleep, deep sleep, and then REM. As you move through the cycle, your sleep phases will usually reduce the amount of deep sleep and increase the amount of REM sleep. A restful night of sleep may end in your body skipping the deep sleep cycle. This is because the deep sleep cycle is harder to wake up from. If you find it easy to wake up and you feel refreshed, then you can assume that you got a pretty good night of sleep and that your body was able to complete a healthy number of cycles.

What Are the Benefits of Sleep for Your Body?

While we don’t know every reason that sleep is required for the body and mind, there is no question it’s essential for healthy functioning. 

These are just a few benefits that you get from sleep:

• Remove Waste: When you’re sleeping, your brain flushes out waste, maintaining healthy brain function. The waste products that are removed from the brain are potential links to neurodegenerative conditions like Alzheimer’s.
• Improved Memory Retention: Your brain can consolidate your memories while you’re sleeping, making connections, forming long-term memories, and making it easier for your brain to retain information in the future.
• Dreams: Dreams occur while you sleep, particularly during the REM stage. Dreams are thought to have some cognitive benefits.

The clear need for sleep is made even more obvious when you’re sleep deprived. Sleep deprivation can cause a number of undesirable side effects that can affect your daily life and your long-term health. If you’re not getting between 6 and 9 hours of sleep per night, or if you’re not going through enough sleep cycles, you may experience the following issues.

• Fatigue and drowsiness
• Irritability and mood swings
• Trouble with memory retention
• Lack of focus and inability to concentrate
• Decreased performance at work and other functions
• Increased risk for health risks like heart disease and mood disorders

It’s crucial to make sure you’re getting enough sleep each night.

Ways to Sleep Better at Night

If you find that you’re not sleeping well at night, it helps to establish healthy sleep habits and prioritize your sleep hygiene. The following are approaches that may help you sleep better at night.

• Cut down on caffeine: If you’re drinking caffeine too late in the day, your sleep cycles may be affected. Caffeine can make it difficult to fall asleep initially, which may cause your sleep cycles to be shorter or give you less time to go through each cycle multiple times. It’s a good idea to stop your caffeine intake before the late afternoon hours. Of course, everyone has a different tolerance level, so your results may vary.
• Exercise: When you exercise regularly, your body may spend more time in the deep sleep phases so your muscles can repair and grow. Keep in mind that exercising earlier in the day is generally better for your sleep cycle. If you exercise too close to bedtime, it may be harder to fall asleep with the increase in energy.
• Prioritize sleep: Sometimes you may stay out extra late or do something to alter your sleep schedule. Obviously, life happens, and you can’t always avoid this, but it does alter your sleep phases. When you’re sleep deprived, your body may put REM sleep on the back burner for a few nights and prioritize deep sleep to repair your body first. This is known as REM rebound. 
• Watch alcohol intake: If you’re having alcohol at the end of the day, try to limit consumption to no later than 4 hours before bed. If you drink too close to bedtime, you may fall into light sleep more easily, but your deep sleep stages may be interrupted.
• Optimize your sleep environment: Make sure your sleep environment is optimized to promote deep sleep. Keep your room dark, cool, and free of noise. Also, make sure you have comfortable bedding to help you fall asleep at night.

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