Why We Sleep by Matthew Walker [Actionable Summary]

This is a comprehensive summary of the book Why We Sleep: Unlocking the Power of Sleep and Dreams by Matthew Walker. Covering the key ideas and proposing practical ways for achieving what’s mentioned in the text. Written by book fanatic and online librarian Ivaylo Durmonski. Supporting Members get access to downloadable worksheets.

The Book In Three Or More Sentences:

A book about why you should go to bed early and never, by no means, deprive yourself of sleep because some nasty side effects might/will occur. Some of these are: you become less effective, less productive, less friendly, attractive, and even more vulnerable to diseases. Matthew Walker, a.k.a. the sleep dude. Talks in length about various researches he and his friends did in the field of sleep. The text mainly aims to scare you by showcasing disturbing facts about people who are not getting enough sleep.

The Core Idea:

The main idea of the book can be summarized in just one simple sentence: Get regular doses of sleep or you’ll die. According to the contents of the book, you need around 8 hours of a good night’s sleep every 24 hours to recharge and unwind from the daily challenges. Not sleeping will make you fat, unproductive, and unable to focus. Also, it can even lead to developing Alzheimer’s disease. The author tested it.


  • Every living creature on the planet has a sleep-wake cycle which is heavily influenced by the sunlight.
  • We dream to deal with the emotional problems we face during the day.
  • Regularly depriving yourself of sleep will lead to some nasty consequences.

5 Key Lessons from Why We Sleep:

Lesson #1: Sleep is The Fourth Biological Drive

There are some things we simply can’t go without. The so-called biological drives.

These internal motives are present to make sure we, humans as a whole, won’t die and humanity will continue to exist. And while people mostly talk about the following three: hunger, thirst, and the desire to reproduce. Sleep – the fourth biological drive as proposed in the book – is equally important.

But why do we have a need to sleep?

If you’re not a scientist, you’ll most probably say: “Because I’m tired and I need to rest. OK?”

And guess what? You’ll be absolutely correct.

But the science behind our desire to go to bed is a bit more complicated than, “I’m tired.”

There are two main reasons we periodically enter a state of deep coma that looks a lot like death at times: circadian rhythm and sleep pressure.

Understanding how these two operate inside your body might help you have a better night’s sleep.

So, here they are in short:

  • Circadian rhythm: Every living creature on the planet has some sort of sleep-wake cycle. For humans, that’s approximately twenty-four hours. It will come to no surprise that this routine is heavily influenced by the sunlight. Our body evolved to operate during the day – when there is natural light – and to rest when there’s none. We’re basically in sync with mother nature. When there is no light our body produces melatonin, chemical signaling that it’s time to sleep. However, keep in mind that this day-night rhythm is not universal. There are folks who are wired to crave darkness and tend to have a hard time waking up in the morning. We call these people night owls.
  • Sleep pressure: Every second you’re awake, a chemical called adenosine is compiling up in your brain. The concentration of this substance is increasing your desire to sleep – scientists call this sleep pressure. But there is a way to pause the effect of this chemical by consuming a quite popular beverage: caffeine. Caffeine blocks the sleeping signal for around 7 hours, tricking the brain into thinking that you don’t need to go to bed. How neat, right? However, if you regularly try to fool your body and mind by consuming caffeine, energy drinks, and alcohol, you’ll confuse your circadian rhythm and eventually feel a lot worse.

The non-scientific takeaway from the above is this: Figure out what type of person you’re – a morning lark or a night owl – reduce the intake of stimulating substances, and find a job that’s aligned with your natural circadian rhythm.

“…we human beings are “solar powered.” Then, as light fades, so, too, does the solar brake pedal blocking melatonin. As melatonin rises, another phase of darkness is signaled and another sleep event is called to the starting line.” Matthew Walker

Lesson #2: We Don’t Just Sleep, We Cycle Through Two Distinct Types Of Sleep

We approach sleep as its this calm, relaxing, not requiring any movement, singular activity. And this is usually what sleep is. But have you ever woken up in the middle of the night, soaked in sweat, terrified of what you’ve dreamed of? Or, the opposite, you slept so deep, that you dreamed nothing?

Both of these things are possible because there are two stages of sleep: REM and NREM sleep.

  • REM: This is an abbreviation for rapid eye movement. The brain activity here is almost identical to when we’re awake. In this stage, we dream.
  • NREM: This means non-rapid eye movement. Basically, a dreamless sleep. During this stage, we’re calm, relaxed and the heart rate is slow and regular. There are four sub-stages of NREM Sleep: from 1 to 4, where 4 is the deepest form of sleep.

These two types of sleep are constantly battling for dominance throughout the whole night when you’re cuddling with the pillow. But despite the fierce war, each stage lasts for around 90 minutes.

According to the book, this is how a typical night looks like for the average person – with the percentage showing the balance between NREM and REM during the particular stage:

  • Cycle 1: NREM (80%) -> REM (20%)
  • Cycle 2: NREM (70%) -> REM (30%)
  • Cycle 3: NREM (60%) -> REM (40%)
  • Cycle 4: NREM (50%) -> REM (50%)
  • Cycle 5: NREM (40%) -> REM (60%)

Initially, in cycle 1, NREM is occupying the majority of the first 90 minutes. Later, there’s a shift – we start to dream more.

Wondering why there is such a complex system for something so simple?

The author’s theory is that we cycle between these two stages, completely different from each other, to defragment our brains and properly process the information we’ve obtained during the day. NREM sleep removes the fluff, sort to speak, while REM sleep stores and strengthens the important stuff.

But not so fast. I have a theory on my own. My logic here is that we cycle between these stages to give our mind and body the opportunity to wake up if there’s a potential threat. After all, if all had was deep sleep, we would never wake up if there was an emergency.

And lastly, if you’re wondering which type of sleep is more important, the answer is simple: both. We equally need NREM and REM sleep to function properly.

Hey there, sorry to interrupt…

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