How sleep works

Before you can tap into improving your sleep, you want to understand how sleep actually works. What happens while you’re in the bed? What will your brain do? What will happen shortly after you drop off and what happens before you wake up? You’ll find an answer to all of these questions in the subsequent paragraphs.

How we sleep

If we want to understand what our body does when asleep, we need to understand that our brain emits different frequencies of waves. While delta waves — the lowest frequency — indicate very deep sleep, beta waves — one of the highest frequencies — indicate alertness. When we are alert and highly focused, for example when writing or memorizing something, our brain is emitting beta waves. During sleep, our brain oscillates between beta and delta waves. 


Most of us believe sleep is a process of our body calming down to a maximum level until we have achieved a delta-wave-like frequency, remain there for most of the time and finally become more alert and wake up. Well, that’s not true. The truth is quite the opposite: We go through all of the phases, from light to deep sleep — up to six times. Hence, we sleep in cycles, each lasting approximately 90 minutes. Understanding these sleep cycles and phases of deep sleep and light sleep is the key to managing your sleep better. To make this veiled phenomenon a bit clearer, let us visualize it. Researchers map sleeping behavior in so-called hypnograms:


1: The spectrum between two extremes: REM vs. (deep) Non-REM stage 3 and 4 sleep

All that matters is understanding the spectrum, i.e. the polarizing relationship, between REM and stage 3 / 4 sleep. The rest can be inferred logically. REM Sleep is often regarded as the ‘deepest’ sleep, even though the truth could not be farther from that. Our brain is very active during REM-phases and emits a frequency which is usually between alpha and beta. We dream during REM-phases and the increased cognitive activity is indicated by our eyes moving very quickly — thus the name Rapid Eye Movement (REM). While REM sleep still remains an arcane phenomenon, it is said that mental recovery is highest during this stage. During deep sleep, our brain goes down to a delta brain wave frequency and our breathing as well as our heartbeat slow down to a minimum level. Muscle relaxation also peaks during deep sleep and important hormones, such as growth hormones, are released during that time. Therefore, it is often stated that deep sleep is for physical recovery. 

One key takeaway is to get up during stage 1 or REM sleep, not when your body is in deep sleep. If your brain is on delta waves, waking up and directly being able to think sharply is impossible. Moreover, your REM phases extend during later cycles of sleep, while your stage 4 phases usually disappear after the first two sleep cycles. This implies that to recover mentally, you need to sleep longer. Short sleep might give you enough time to recover physically, but will fail to provide you with enough mental recovery, especially if you just had a difficult day. 

2: Sleep Cycles

Sleep happens in cycles of approximately 90 minutes. Note that deep sleep typically happens only in the first two cycles as indicated in the hypnogram, while REM stages are often followed by periods of being wake — especially after the first two cycles. Waking up during the night is completely normal, and if it is below 2–3 minutes, we usually do not remember it. Moreover, while those 90-minute cycles vary between people and tend to get shorter for each cycle, they usually stay the same for individual probands. Therefore, knowing how long your cycles are matters. This will help you to get up during stage 1 sleep or REM sleep. That implies that you should time your sleep and only get up after a 1,5h cycle. If you notice that you still feel dizzy or tired, you might want to experiment with cycles of 1h 25m or 1h 35m as lengths of sleep cycles differ between individuals.

Having gained an understanding of sleep cycles and brain waves, you’re now ready to dig into your hormones and circadian rhythm while sleeping.

You might want to try the following:

If you have a healthy circadian rhythm your sleep will be fairly regular. This allows you to make use of the following action steps.

First, get up when you are actually awake. Track your sleep cycles and experiment with different times. While there are a myriad of apps out there, we do not recommend a tracking app. Firstly, sleeping directly next to your phone is not a healthy thing to do. Secondly, those apps are not yet perfectly accurate. What you can do instead is very simple: Track when you

  1. Go to bed
  2. Get up in the morning
  3. How long it takes you to fall asleep
  4. How you feel during the day and how easy it was to get up

You might want to go to bed at 10.45 pm and get up at 6.30 am. If you need approximately 15 minutes to fall asleep, you will have slept 7 hours and 30 minutes. Divide this by 5 (as there are usually 5 sleep cycles for that length of time) and you get exactly 1 hour and 30 minutes. Bingo — that’s it already! And for most, it will most likely be that easy. For those who do not feel fit after getting up exactly 7 hours and 30 minutes, try 7 hours and 40 minutes or 7 hours and 50 minutes. Continue adding 10 minutes to your sleep until you feel awake. If you finally do, repeat it to make sure that sleeping time works for you. Again, divide by 5 to find out how long your sleeping cycles are. If you need 8 hours, your sleeping cycle will likely be 96 minutes. Getting up during a phase of deep sleep can be really detrimental and might affect your hormone cycles throughout your entire morning, leading to less energy and alertness. Therefore, getting up earlier, if it prevents you from falling into another phase of deeper sleep, often results in you feeling more alert.

Second, if you need to mentally perform during the next day, make sure to sleep as long as possible. Especially when there is an important presentation the next day, a difficult exam or anything that requires mental preparation, we tend to pull all-nighters and sleepless. Yet, during those periods you should pay special attention to the amount of sleep you get. Aim for 8 hours, which allows for 5 sleep cycles when factoring in some time to fall asleep and get up. As your mental recovery tends to be highest during the later stages of your sleep, sacrificing on those can come with a high price.

Third, if physical recovery is important during the next day, because of a work out, for example, make sure to wind down properly and go to bed early. If you go to bed later than you usually do, your melatonin secretion will kick-in too late and your growth hormone release might be deferred, which leads to even more disturbed sleep. You want to prevent that, especially after heavy work-outs. Interestingly though, to recover physically you will not need to sleep that long. As we had observed in the hypnogram, our physical recovery seems to happen during the first two sleep cycles, which allows us to sleep less.

Fourth, never sleep less than 6 hours. The amount of sleep you need is influenced by your genetics and is highly individual. Some of you might cope with 6 hours, but this is rather the exception than the rule. If you wake up naturally or feel alert and fit during the day, your current sleeping duration is fine. Sleeping less than you need to, though, can have severe effects on your overall health, such as higher risk of depression, cancer and Alzheimer’s.

Fifth, sleep no longer than 8 hours. There are a couple of superbly interesting research papers on the duration of sleep and mortality rates suggesting that longer sleep rates are connected to higher mortality. A valid meta-analysis comprises the results of analyzing a million probands for up to 50 years. The two most interesting graphs are also included below: