What is a sleep cycle?


The simple, everyday act of sleeping is not as straightforward as it once was. We either fail to get enough sleep or we find our bedtime haunted by insomnia or wakefulness. When it starts to feel like it’s impossible to get a good night’s sleep, it might actually be time to take a closer look at your sleep cycle.

What is a sleep cycle 1Photo: Active Health

What goes on during the sleep cycle?

Falling asleep isn’t as simple as just closing your eyes and heading straight to dreamland. In fact, your brain and body go through various stages of Rapid Eye Movement (REM) and Non-REM (NREM) sleep that differ according to how deep and restful they are. The sleep cycle is basically made up of four such stages and spans about 1.5 to 2 hours, so you typically go through several cycles throughout a standard night's sleep. Here’s a breakdown of what happens in each cycle.

What happens during NREM Stage 1?

This stage occurs when you are just falling asleep. At this stage, your sleep is light and easily disturbed by external influences. While your body is starting to relax into sleep and your brain activity slows down, some people may experience hypnic jerks or feel a free-falling sensation that jolts them back awake.

What happens during NREM Stage 2?

Once you have gotten past stage 1, your heart rate will begin to slow even more and your core body temperature drops, bringing you to stage 2 of NREM sleep. You are experiencing a deeper sleep than before, and it will be harder to wake you up. This stage is usually the longest in the sleep cycle, making up almost half the entire sleep cycle.

What happens during NREM Stage 3?

This is the deepest stage of NREM sleep, so it will be the hardest for you to wake up at this stage. You experience the most restorative sleep at this stage, which is essential for ensuring that you feel well-rested and alert the next day. Restorative sleep is also crucial for your well-being as it is during this type of sleep when growth hormones are released to help your body and immune system recover. Unfortunately, restorative sleep isn’t the only thing that happens at stage 3 – some people may experience parasomnias such as sleep paralysis, sleep talking and bed-wetting.

What happens during REM?

After stage 3 of NREM sleep, your sleep cycle eases back into stage 2 and then stage 1 before entering REM sleep. REM sleep is when you actually dream, so your brain and eye movements are far more active. In REM sleep, you are no longer sleeping as deeply so it will it be easier to wake you up but being woken up at this stage will usually leave you feeling disoriented and groggy.

Clearly, sleep isn’t as simple as just dreaming and recovering from the day’s activities, since these only happen at specific stages in your sleep. To further complicate matters, each sleep cycle isn’t exactly the same in terms of how long you spend in each stage. For example, the amount of time you spend in deep sleep during stage 3 depends on age, with younger children spending longer in stage 3 than adults.

The time of the night also affects how much NREM and REM sleep you are getting – the earlier it is, the more NREM sleep you get and vice versa. Finally, the number of sleep cycles you experience also depends on your age. Younger children sleep up to 10 hours while adults usually only need 6-8 hours. This is a result of the body’s circadian rhythm, which is responsible for creating sleep cycles.

What is a sleep cycle 2Photo: Active Health

How are sleep cycles created?

Sleep cycles are regulated by your body’s circadian rhythm, which is essentially a series of changes in your body’s physical and mental functions in response to changes in your external environment, primarily changes in light and darkness. These circadian rhythms don’t act on their own but are in fact controlled by your internal “body clock”, which is responsible for keeping your body functions working normally. Hence, your sleep cycles are dependent on both your body’s biological clocks and also external environmental factors that can affect your circadian rhythm.

Understanding both of these is important as firstly, biological clocks are responsible for your overall health and well-being and can affect issues such as your weight and mental health. Secondly, understanding your circadian rhythm is key to managing environmental influences that may be disrupting your sleep cycles and costing you precious sleep. While learning how your biological clock works can be tricky to do without a professional’s help, regulating your circadian rhythm is relatively more straightforward and easier. All you need to do is watch out for the following external influences on your sleep cycle and manage them well.

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External influences on our sleep cycles

• Exposure to light

As mentioned previously, light has the biggest influence on your circadian rhythm as it affects your body’s perception of day and night and hence affects how ready you are for sleep. Exposure to too much light at night can trick your body into thinking it is still daytime, so you may end up experiencing trouble falling asleep. Thus, reducing your exposure to light when it’s nearing your bedtime can help to correct your circadian rhythm. Dimming your lights and turning off your digital devices can help with this.

• Bedroom environment

Your bedroom environment also has a huge effect on your sleep cycle. You will naturally get better sleep in a comfortable bedroom as your body will be more relaxed. The noise levels in your room also affect your sleep – disruptive noises like smartphone notifications can wake you up, especially when you are in the earlier stages of NREM sleep. Also, the temperature in your room is another important factor that affects your sleep cycle, as temperature has an impact on your circadian rhythm. Cooler temperatures usually help you sleep better as it helps your body cool down to transition into the deeper stages of NREM sleep.

• Irregular bedtimes due to lifestyle

As a result of your naturally functioning circadian rhythm that responds primarily to light, trying to fall asleep in the day or stay up at night can be really difficult. This is why people who work the night shift tend to feel exhausted at work yet may experience insomnia when trying to sleep during the day. People who travel across different time zones will also have problems with getting enough sleep, as their circadian rhythms are unable to adapt to the new time zone on such short notice.

• What you consume

Alcoholic beverages and caffeinated drinks definitely have a disruptive effect on your sleep cycle. Alcohol may make you feel sleepy at first, but it makes it harder for you to stay asleep and can cause wakefulness. As for caffeine, it has the effect of decreasing the time you spend in NREM stage 3 as well as REM sleep, so you get a lot less restorative sleep and end up feeling exhausted the next day.

• Medical conditions

Chronic pains can severely disrupt your sleep cycles as the discomfort will constantly wake you up whenever you are in a lighter stage of sleep. As a result, the amount of sleep you actually get will be greatly limited.

• Mental conditions

Stress and anxiety make it hard for your body and mind to relax sufficiently to enter NREM stage 3, so instead of deep and restorative sleep, you get more REM and light sleep. As a result, it will be hard for your mind to let go of the stress and anxiety, which only exacerbates the problem. As such, it can be helpful for you to consider engaging in stress-relief activities before bedtime, like yoga or meditation for example. To get some recommendations on suitable pre-bedtime activities you can do to de-stress, speak to our Active Health Coaches at Active Health Labs located island-wide.

What is a sleep cycle 3Photo: Active Health

Maintaining a healthy sleep cycle

• Sleep and wake up at regular times

Since your sleep cycle is closely affiliated with your circadian rhythm, adhering to a regular bedtime and waking time will help to regulate your sleep cycle, so you can maximise the amount of restorative sleep you get.

• Don’t hit the snooze button

Hitting snooze for some extra sleep won’t do you any good as it disrupts your circadian rhythm by unnecessarily extending your sleep, so get up at the first alarm and let your body get used to waking up this way.

• Track your sleep cycles

If you constantly experience problems with maintaining a healthy sleep cycle, tracking your sleep cycles by using wearable sleep trackers can help you better manage this. Sleep trackers can gather your sleep data based on your heart rate and other variables and help you analyse your sleep patterns.

Sleep is a lot more complicated than we think. By understanding the way our sleep cycles work and how they are affected by our circadian rhythm, we can better overcome the complexity of our sleep-related issues. This way, we can help ourselves attain the quality of sleep we rightfully deserve!

► READ: More articles and tips to Rest Better

Topics: Sleep, Rest Better