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.

Worksheet: Download the interactive sheet for taking notes.

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.

Lesson #3: Not Sleeping Can Kill You. For Real!

Modern people approach sleep as something annoying. After all, you can’t hustle and do social media while you’re snoozing. That’s why people try to life-hack sleep.

We consume various stimuli to keep ourselves awake so we can do more “important” stuff while forgetting that good night sleep is as equally important as eating and exercising, if not even more.

In Why We Sleep, Matthew Walker does a pretty good job at explaining the various malfunctions sleep deprivation can cause to our body and mind. His main goal, I think, is to help us understand that sleep should be something non-negotiable.

Here are a couple of disturbing facts from the book that might occur if you’re getting too little sleep followed by a few interesting notes about sleeping.

Alarming facts about not sleeping:

  • Fact 1: “The shorter your sleep, the shorter your life span,” says Matthew Walker. This statement is not backed by any scientific evidence but not sleeping can make you a lousy driver and therefore increase the chances of a fatal ending in traffic.
  • Fact 2: Consuming alcohol to persuade yourself to sleep is a bad practice. Alcoholic beverages mess up your REM sleep and you get fragmented sleep.
  • Fact 3: With age, our sleep efficiency declines. This is mainly because of our frequent visits to the bathroom. A simple fix will be to reduce the intake of fluids before going to sleep.
  • Fact 4: Studies confirm that a lack of sleep can lead to a lot of nasty outcomes. Here are some mentioned in the book: “diabetes, depression, chronic pain, stroke, cardiovascular disease, and Alzheimer’s disease.”
  • Fact 5: You can’t sleep it off. According to the author, even if you get enough sleep to recover from last night’s party, the brain cells that have died during the sleep deprivation will never heal.
  • Fact 6: You start to gain weight if you don’t get enough sleep. This is caused by two hormones that are released in your body: leptin and ghrelin. In short, the imbalance between the two increases your level of hunger causing weight gain.
  • Fact 7: Your immune system is getting weaker when you’re sleeping less. On top of that, your libido also suffers.
  • Fact 8: Sleeping pills are bad for your health. Don’t take them.
  • Fact 9: A lack of sleep will reduce your reaction time and also sabotage your performance during the day. Additionally, it can lead to depression and a nasty mood.

“After being awake for nineteen hours, people who were sleep-deprived were as cognitively impaired as those who were legally drunk.” Matthew Walker

Interesting facts about sleeping:

  • Fact 1: During REM sleep our body gets paralyzed by the brain. The reason? To prevent us from executing on our dreams. If we’re not paralyzed during REM sleep, we’ll most probably get up and walk around (sleepwalking).
  • Fact 2: Sleeping helps us improve. When we’re learning or practicing something and we stop, our brain will continue to work on these tasks on the background. This passive learning process gets even stronger when we shut our eyes.
  • Fact 3: Sleep fuels our creativity. During sleep our brains build connections, nurturing our problem-solving skills and imagination.
  • Fact 4: The main function of dreaming is to help us resolve past, or current, emotional problems. In the book, the author states the following: “Sleep, and specifically REM sleep, was clearly needed in order for us to heal emotional wounds.” But there is a catch, you need to dream about your troubles to get over them.
  • Fact 5: There is this thing called lucid dreaming where you’re completely aware of what you’re dreaming. In this state, you can manipulate the dream and decide what to do instead of simply going with the flow of the dream. How you can do that? It’s not very clear and apparently, only around 20% of the world’s population are lucid dreamers.
  • Fact 6: Since the temperature decreases when the sun sets, and for thousands of years we have slept in the wilderness, you’ll fall asleep easier in a colder room – around 65 degrees Fahrenheit (18.3°C).
  • Fact 7: The most popular sleep pattern is monopolistic – where we allocate around 7 hours per day for sleeping. However, hunter-gatherers were favoring the biphasic pattern. This model also includes taking a third of your day sleeping followed by a must-have nap of around 30 minutes during the day.

Lesson #4: The Main Reason We Sleep And Dream Is To Fix What Was Done During Our Awake Hours

How often do you hear people say: “Don’t worry about it, just sleep it off.”

Quite often, right?

Well, that’s because sleeping helps us recover from both physical and emotional problems.

We need to sleep to recover from the busy day, put our brain into rest and deal with our emotional problems.

But even though the title of the book is Why We Sleep, the text inside it’s mainly about the importance of sleeping and what can potentially happen if you don’t get a good 7 to 8 hours of sleep regularly.

That being said, there was nothing really new in the book about why we actually need to sleep.

The main reasons we need to lay down and shut our eyes are surely things you already know:

  • To give your body and brain time to recover.
  • To reflect on the things that have happened during the day.
  • To heal from the emotional burdens and physical injuries.

Imagine sleep as turning off your computer. You probably work on your laptop for a few hours each day. During that time you open various programs, sites, apps, even games. All of these are processed by the RAM memory. The more things you have going on, the harder for your machine to handle them. At some point – as I’m sure that this happened to you at least once in your life – the laptop crashes and you have to restart it.

Similar things happen to us.

We talk to people. We exhaust our bodies by walking and doing other physical activities. We think. We make decisions. We try to be polite with people we don’t really like. All of these things pile up. That’s why it’s getting harder for us to make decisions with each minute we’re awake. At some point, if we had a really busy day, we even stop listening to our spouse. That’s when the shit hits the fan. Our partner gets angry at us and the whole day is ruined. All of this could have been avoided if we went to bed early.

So, the answer to the question “why we sleep” is rather obvious: Because both our body and mind are tired. In addition to that, I’ll add: Sleep is the state we need to enter to restore our health and fix the emotional traumas that troubled our day.

“Many of the explanations for why we sleep circle around a common, and perhaps erroneous, idea: sleep is the state we must enter in order to fix that which has been upset by wake.” Matthew Walker

Lesson #5: There Are Things We Can Do To Improve Our Sleep Hygiene

Obviously, not sleeping is bad, but what we can do?

According to the author, a lot.

While going early to bed is the easiest thing you can do, companies, governments, and educational institutions also need to participate if we want to improve our time in bed and with this the well-being of the nations.

There’s actually a framework presented in the book that both individuals and organizations can follow to improve the sleep hygiene of society.

First, let’s see what can be done by the government:

  1. Sleep education: There are classes about our health and about physical activities, but there aren’t such for resting. “Develop a simple educational module in schools,” says the author. This way we’ll raise our children with good sleep habits.
  2. Flexible working hours: This is already happening. Freelancing allows digital nomads to work depending on their own personal circadian rhythm. They don’t have to get up at 7 AM and drag themselves to the office. If they’re night owls they can rest and work from noon. Similar changes should occur in big corporations. Even though I don’t believe it’s possible, if the working hours are tailored to the individual, not the other way around, where the individual adjusts himself to the working hours of the firm, probably productivity will skyrocket.
  3. Public campaigns: There are educational campaigns about cancer, about HIV, about drugs, but there aren’t such for better sleep. Well, if a lack of sleep can cause Alzheimer’s, as stated in the book, we should definitely reconsider our health care budget.

Secondly, let’s observe what we, the people, can do to improve our sleep quality.

The tips below are based on the information in the book which is actually from Medline Plus Magazine from summer 2012:

  1. Stick to a sleep schedule. Create a sleeping habit by going to bed and waking up at the same time, every-single-day. Oversleeping on weekends feels good but it ruins your progress during the week.
  2. Exercise, but don’t do it before going to sleep. Your body needs at least 3 hours to calm down after a workout. Don’t train and hit the sack directly.
  3. Avoid caffeine and nicotine. The effect of stimulating beverages like coffee can take as long as eight hours to fully wear off.
  4. Avoid alcohol before going to bed. Heavy drinkers have issues with sleep. They think drinking helps but only initially. Usually, their sleep gets fragmented because of overuse.
  5. Avoid eating and drinking plenty of water before going to sleep. Your system needs time to process the food you ate. If you go to bed right after a rich dinner, you’ll have a hard time falling asleep. Similar interruptions happen if you drink a lot of fluids – you’ll get up frequently during the night.
  6. Avoid taking pills. Especially sleeping pills. OK, some people might need medicine for their blood pressure or something similar, but even if your health depends on it, take your pills early in the evening. Of course, consult first with your doctor.
  7. Don’t take naps after 3 PM. Naps are good but if you fall asleep on the sofa around 20:00 o’clock, you’ll be counting sheeps when you go to bed.
  8. Relax before going to bed. Make sure you’ll have enough time at the end of the day for relaxing activities – reading a book or listening to music. This will set the mood for sleeping.
  9. A hot bath before bed might help. Taking a bath will help you relax. Along with that, your body temperature after the shower will decrease helping you feel sleepy.
  10. Diss the gadgets and dim the lights in your bedroom. Bright lights and cell phones should be forbidden. Light, natural or artificial, will cease the production and release of melatonin in your body. The chemical you need in your system to feel sleepy. Additionally, you should also make your bedroom colder. We sleep better in cold rooms, not in hot ones.
  11. Expose yourself to sunlight. Daylight regulates your sleep patterns. Make sure you’re outside for at least 30 minutes a day.
  12. If you can’t fall asleep, do something. If you’re laying in bed and if you can’t shut down, get up and do something relaxing. I personally recommend reading a book.

“I believe it is time for us to reclaim our right to a full night of sleep, without embarrassment or the damaging stigma of laziness. In doing so, we can be reunited with that most powerful elixir of wellness and vitality, dispensed through every conceivable biological pathway.” Matthew Walker

Actionable Notes:

  • Take naps: Usain Bolt, the 100-meter sprint gold medalist, takes plenty of zzz’s throughout the day to recharge. Even though you probably won’t try to break the world record, taking a nap is surely something that will help you feel better. Sometimes even a quick 20-minute snooze can significantly increase your memory. Still, remember tip 7 from above: don’t take naps after 3 PM or you’ll have trouble falling asleep at night.
  • Lower the thermostat: Besides saving money on your electricity bill, you’ll also sleep better. There’s a correlation between temperature and sleepiness. Since for decades, humans slept outside, the body evolved to adore lower temperatures. You should aim for a temperature of around 65 degrees Fahrenheit (18.3°C) for your bedroom.
  • Give yourself more opportunity for sleep: There’s a difference between time slept and sleep opportunity time. If you go to bed at 11 PM and you need to wake up at 06:00 AM, this doesn’t mean that you’ll sleep full 7 hours, not at all. You’re not counting the time you need to actually fall asleep and the trips to the bathroom in the middle of the night. Go to bed early and give yourself more opportunity to sleep.
  • Keep a sleep diary: This simple method will help you improve your sleep hygiene and decrypt your dreams. You simply need to write the date, the time you went to bed, at what time you woke up, and what you were dreaming. Additional things that might help are how many cups of coffee you had during the day and whether or not you exercised. These notes will help you track down harmful patterns you do during the day so you can later make adjustments.
  • Why bother waking up? Life emerged from sleep. When we were in our mother’s womb, we were first asleep. Later, we woke up. For what? That’s exactly what you should ask yourself. Though the question in the book was asked in a different context, it’s surely something that will help you evaluate your daily actions. So, ask yourself: Why bother waking up? There should be something that inspires you. Something that will make you proud to be a part of this world. Find it.

Commentary and My Personal Takeaway

Personally, I don’t know why people are so crazily obsessed with this book. Everybody is rating this book with 5 stars. Probably I’m stupid and I can’t see what others are seeing.

I mean, yeah, there are valid points in the book. Some interesting insights from various experiments related to sleep. Also, suggestions that can potentially help us increase our wellness. However, the majority of the text feels like blather.

Oh, and one more thing: the critique of the book here explains how some of the facts mentioned in the book aren’t really backed by science. If you don’t have an academic interest in the subject, it probably won’t matter to you, but it surely makes you question everything written inside.

But let’s go back to my commentary…

The chapters in the book, which are abnormally long and hard to navigate, usually go like this: “Hey, not sleeping will make you fat, here, we tested it.” But while the data might be correct, throwing 15 pages of comparisons and facts that no one understands just to show us that, yes, sleep deprivation can cause some nasty complications and suboptimal performance is the wrong approach. At least that’s my opinion.

Something else I didn’t quite like is the author’s constant explanation that sleep is making people better. “Hey, people who are getting more sleep are smarter”, “People who sleep more are better drivers and don’t hit other folks”, “People who rest are more productive,” and so on.

Well, duh! We all know that.

I don’t think you should be a scientist to say that sleeping a bit more can help you concentrate better and become more productive. A 7-year-old can make the same conclusion.

My main takeaway from the book is really simple: There’s a fine line between good night’s sleep and laziness. Don’t compromise on sleep but also make sure you don’t spend half of your day in bed.

Notable Quotes:

“There are many things that I hope readers take away from this book. This is one of the most important: if you are drowsy while driving, please, please stop. It is lethal.” Matthew Walker

“Sleep is the single most effective thing we can do to reset our brain and body health each day – Mother Nature’s best effort yet at contra-death.” Matthew Walker

“Practice does not make perfect. It is practice, followed by a night of sleep, that leads to perfection.” Matthew Walker

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