Why We Sleep Summary

Sud Alogu
6 min readAug 13, 2020


Why We Sleep by Mathew Walker is about the science of sleep. What happens when we sleep, how are our minds are shaped by the quality of our sleep? What are the repercussions to not sleeping well?

Imagine you read a headline titled “Amazing Breakthrough” — that promised a new treatment that extends your lifespan, memory, and makes you more creative and attractive. It also keeps you slim and lowers your food cravings. This breakthrough protects you from cancer, dementia, colds and the flu. It lowers your risk of stroke and heart attack, and diabetes. You will feel happier, less anxious, and less depressed.

Are you interested?

That is the promise of sleep, according to Mathew Walker. Sleeping well brings all those benefits, and not sleeping well will bring an avalanche of problems related to your physical and psychological health.

How much Sleep?

If you sleep less than 6–7 hours a night, your immune system will be demolished, and this will more than double your risk of cancer.

Car accidents caused by drowsy driving exceed those caused by alcohol and drugs combined.


We are starting to understand the most controversial conscious experience: the dream. Dreaming provides humans with many benefits, including a neurochemical bath that soothes painful memories and a virtual reality space in which the brain melds past and present knowledge, inspiring creativity.

As when you are awake, the sensory gate of the thalamus swings open during REM sleep. But it is a different kind of gate. Rather than experiencing sensations from the outside world, you will feel a rush of emotions, memories, and motivations play out in a preposterous theater.

Your brain is an information processing machine. During wake state, you are receiving information. NREM sleep is when you reflect (store and strengthen raw ingredients of new facts and skills), and REM sleep is when you integrate it all (the raw ingredients are interwoven with past experiences, helping you build a more accurate model of how the world works, including novel insights and problem solving abilities).

The damage you incur to yourself physically and mentally from one night of bad sleep dwarf an equivalent absence of food or exercise.


Melatonin gives the official instruction to begin the process of sleep, but does not participate in the sleep race itself. Thus, melatonin is not a powerful aid on its own, at least for healthy non-jet lagged individuals.

For every day you are in a different time zone, your suprachiasmatic nucleus can only readjust by about one hour.

Even though users of sleeping pills sleep faster at night, they wake up with fewer memories of yesterday.


Caffeine has an average half-life of 5–7 hours. If you drink coffee after 7.30 p.m, then by 1.30 a.m, 50 percent of the that caffeine may be active and circulating throughout your brain tissue. So, by 1.30 a.m, you are only halfway to cleansing your brain of the caffeine you had after dinner.

Caffeine works by latching on to adenosine receptors in your brain (adenosine makes you sleepy). Caffeine effectively block adenosine receptors, preventing the feeling of sleepiness.

Types of Sleepers

The peak of wakefulness arrives early in the day for some people. These are the “morning types”, and they make up 40 percent of the populace. Others are “evening types” and are around 30 percent of the population. They prefer to sleep late and wake up late the following morning, or even in the afternoon. The remaining 30 percent are somewhere in between, with a slight leaning towards eveningness.

You make know these types as “morning larks” and “night owls.” Night owls find it hard to sleep early at night, no matter how hard they try. Their prefrontal cortex stays asleep for longer, including the morning hours. The prefrontal cortex controls high-level thought and logical reasoning and keeps our emotions in check. Owlness or Larkness is largely determined by genetics.

Society sadly treats night owls unfairly. One, it labels them as lazy. Two, the way society is scheduled accommodates morning larks much more than night owls. Unfortunately, owls are more chronically sleep-deprived, since they have to wake up with the larks, but they cannot fall asleep early like the larks.


Owls are thus often forced to burn the proverbial candle at both ends. Greater ill health caused by a lack of sleep therefore befalls owls, including higher rates of depression, anxiety, diabetes, cancer, heart attack, and stroke.

Napping is an evolutionarily imprinted behavior that is a normal part of the daily rhythm of life.


Not taking naps can lead to physical ailments.

Wish Fulfilments

Sleep is not like a bank. If you do not sleep the very first night after learning, you lose the chance to consulate these memories, even if you get “catch-up” sleep later.

When it comes to dreams, Freud was half right and 100 percent wrong. He thought that dreams came from unconscious wishes that had not been fulfilled. These repressed wishes, if not disguised by the brain, would wake the dreamer up. Thus dreams were a way of disguising repressed wishes and allowing them to pass without waking up the dreamer.

Freud believed that he discovered the decryption key to everyone’s dreams, and offered the paid service of removing this disguise to rich Viennese patients. But the problem was the lack of clear predictions from Freud’s theory. Scientists could not design an experiment to falsify or support his claims. This was Freud’s genius and downfall.

Trauma Recovery

Science could never prove him wrong, which is why Freud continues to cast a long shadow on dream research until now. But a theory that can never be proven true or false will be abandoned by science, which is what happened to Freud and his psychoanalytic practices.

Lucid Dreaming

Cartwright showed that REM sleep or generic dreaming were not sufficient when it comes to resolving our emotional past. Her patients required REM sleep plus dreaming, but a specific kind of dreaming about the emotional themes of the waking trauma. It was only this content-specific form of dreaming that could accomplish clinical remission and give patients emotional closure.

Through an experiment, scientists could prove that lucid dreaming was real. They took pictures of brain activity when participants signaled the beginning of the lucid dream state. Then the sleeping participants signaled their intent to dream about moving their left hand and then their right hand, alternating repeatedly, just like they did when awake. Even though their hands were not moving due to REM-sleep paralysis, they were moving in the dream. At least according to what the participants said upon awakening.

The results of the MRI scans proved that they were being truthful. The same regions of the brain that were active when participants were awake lit up during times when the participants were dreaming.

What Prevents Sleep?

Scientists had gained an objective, brain-based proof that lucid dreamers can control when and what they dream while they are dreaming.

Other than longer commute times and sleep procrastination caused by digital entertainment late at night, there are give key factors that have change how and well we sleep.


(1) constant electric light as well as LED light, (2) regularized temperature, (3) caffeine (discussed in chapter 2), (4) alcohol, and (5) a legacy of punching time cards.

Read The Book

Walker claims that the evidence is so strong regarding alcohol’s harmful effects on sleep that the only advice he can honestly offer is abstinence.

Originally published at https://unearnedwisdom.com.



Sud Alogu

In search of truth and deception.