why we sleep summary

Why We Sleep by Matthew Walker Book Summary & Notes

Disclosure: Some of the links below are affiliate links. This means that, at zero cost to you, we will earn an affiliate commission if you click through the link and finalize a purchase.
Why We Sleep

Published: 28 September 2017 by Penguin Random House

Science book

My Rating

Buy this book on The Book Depository


“The best bridge between despair and hope is a good night’s sleep.”

“Humans are not sleeping the way nature intended. The number of sleep bouts, the duration of sleep, and when sleep occurs have all been comprehensively distorted by modernity.”

“the shorter your sleep, the shorter your life. The leading causes of disease and death in developed nations—diseases that are crippling health-care systems, such as heart disease, obesity, dementia, diabetes, and cancer—all have recognized causal links to a lack of sleep.”

Key Idea #1: The body signals us that it’s night and day through our circadian rhythm and sleep pressure.

To say that someone is asleep, there are universal indicators. First, the loss of awareness of the environment. Second, loss of time-consciousness. Even though we are sleeping, our ears can still “hear” and our eyes can still “see”.

Inside our body lies an internal body clock called the suprachiasmatic (pronounced soo-pra-kai-as-MAT-ik) nucleus which is located deep within our brain. This clock creates a day-night rhythm that determines when you want to be awake and when you want to be asleep. This also controls other rhythmic patterns like eating and drinking, emotions, the amount of urine you produce, metabolic rate.


A chemical substance called adenosine accumulates the longer you are awake. It’s like a barometer in your brain that measures the amount of time passed since you woke up this morning. As the adenosine increases, your desire to sleep also increases. (sleep pressure). It determines when you feel sleepy and thus lay in bed.

Adenosine can be blocked by Caffeine, the most widely used (and abused) psychoactive stimulant in the world.

Caffeine has an average half-life of five to seven hours. It tricks you to being awake despite having high levels of adenosine.

Each person has a different rhythm. Morning larks and night owls have chronotypes determined by genetic fate. If you are a morning lark, your parents are most likely morning people too. Night owls are not lazy people, they just have an unavoidable DNA hardwiring so they couldn’t sleep and wake early.

Key Idea #2: The two stages of sleep fight for brain domination across the night every ninety minutes.

There are two stages of sleep, Non-rapid eye movement (NREM) and rapid eye movement (REM).

NREM sleep is split into 4 separate stages and mostly dominates sleep. Stages 3 to 4 are the deepest stages of NREM sleep. It works by removing unnecessary connections in the brain. It functions as a courier, NREM fires many thousands of brain cells that transfer recent experiences from a short-term storage site of the brain (hippocampus) to a more permanent long-term location. (cortex)

In contrast, the REM sleep or dreaming stage plays a role in strengthening neural connections. It adds details to the memory. REM dreaming removes unwanted information called “parasitic memories”

NREM and REM are like creating a piece of sculpture. To build one, a large amount of clay should be placed to act as a pedestal. (a large quantity of memory is given to the brain each night). The next phase is the removal of unnecessary stuff (NREM stage), then the final touches. (REM). It’s a cycle in an 8 hour time.

Key Idea #3: Sleep is universal.

Every entering a sleep state to fix which has been destroyed by the wake. It is from sleep we are waking up.

Sleep varies from one species to another. Large mammals like elephants require just four hours of sleep a day. Tigers and lions slumber fifteen hours daily.

Not all species experience NREM and REM. Amphibians, insects, reptiles don’t have REM sleep.

Key Idea #4: Sleep improves our well-being.

Sleep improves our learning ability, memorizing skills, and decision-making. Before we acquire new information, sleep prepares the brain to make new memories. After learning, sleep makes those memories remembered through a process called consolidation.

Consolidation is an all-or-nothing event. Not only does it make the memory be retained, but it also saves those memories that you could not remember before sleep.

In learning, if you don’t sleep the very first night after acquiring information, you will lose that chance to consolidate those memories, even if you sleep a lot thereafter.

Sleeping recalibrates our emotional brain circuits which heals our emotional wounds through dreaming. The theory of overnight therapy states that REM-sleeping reaches two critical goals: 1) remembering the details of valuable experiences and integrates them into an autobiographical perspective. 2) helps us forget painful memories that happened throughout the day

Sleeping also helps you control body weight, thus decreasing the risk of having diabetes and other diseases like Alzheimer’s.

Key Idea#5: Sleep distractions and sleep deprivation hurt your sleep.

Artificial light deceives us that it’s still day while it’s already nighttime.

LED devices like iPad block the melatonin, the sleep hormone by 23 % by the light it emits.

Drowsy or being sleep-deprived while driving exceeds those caused by alcohol and drugs combined. There is no scientific evidence that implies a drug, a device, or any amount of psychological willpower can replace sleep.


  • Have a consistent sleep schedule.
  • Wake up at the same time every day. #MindOverMattress
  • Set an alarm two hours before sleeping and start reading a book or listening to an audiobook. Make your room gadget-free so that it won’t distract you from sleep. Try to go outside and have the right amount of sunlight to regulate your sleep patterns.


This science-backed book has changed the way I think about sleep. I now sleep early and wake up feeling better every day. It’s important to have 8 hours of good sleep. The author did a great job of explaining how sleeps works and telling useful stories. My favorite part is that when he mentioned sleep heals the emotional wounds that happened throughout the day. Meaning, every day is a brand new day. I can start all over again!

I would recommend this to people who experience catastrophe sleeping at night, encounters the damage of laziness stigma. It’s time to sleep with no embarrassment.

Thanks for reading! Comment below, I’d love to hear your thoughts!


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Shopping Cart