Why We Sleep – Matthew Walker, PhD

Never have I ever slept so much while reading a book! And, it wasn’t because it was boring but because the book is all about sleeping so naturally, I took many naps. It took me longer than usual to finish because I kept napping, but Matthew Walker said that could happen and he encouraged it.

Despite multiple naps, I learned a lot about why we sleep and how important it is. There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep (and detrimentally impaired when we don’t get enough). 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. We are, as you will see, socially, organizationally, economically, physically, behaviorally, nutritionally, linguistically, cognitively, and emotionally dependent upon sleep.


  1. Routinely sleeping less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer.
  2. Too little sleep swells concentrations of a hormone that makes you feel hungry while suppressing a companion hormone that otherwise signals food satisfaction, which is why you notice a desire to eat more when you’re tired.
  3. If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.
  4. We sleep for a rich litany of functions, plural – an abundant constellation of nighttime benefits that service our brains and our bodies.
  5. Dreaming provides a unique suite of benefits to all species fortunate enough to experience it, humans included. Among these gifts is a consoling neurochemical bath that mollified painful memories and a virtual reality space in which the brain melds past and present knowledge, inspiring creativity.
  6. Night owls are not night owls by choice. They are bound to a delayed schedule by unavoidable DNA hardwiring. It is to their conscious faulty, but rather their genetic fate. However, owls are more chronically sleep-deprived, having to wake up with the larks (morning people). Owls are 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, depression, cancer, heart attack, and stroke.
  7. There is a significant sleep placebo effect of melatonin, which should not be underestimated.
  8. Caffeine is not a food supplement. Rather, caffeine is the most widely used (and abused) psychoactive stimulant in the world.
  9. Humans don’t just sleep but cycle through two completely different types of sleep. They named these sleep stages based on their defining ocular features: non-rapid eye movement (NREM sleep) and rapid eye movement (REM sleep).
  10. Why did evolution decide to outlaw muscle activity during REM sleep? Because by eliminating muscle activity you are prevented from acting out your dream experience. During REM sleep, there is a non-stop barrage of motor commands swirling around the brain, and they underlie the movement-rich experience of dreams.
  11. However, the paralysis mechanism can fail in some people, particularly later in life. Consequentially, they convert these dream-related motor impulses into real-world physical actions.
  12. Most adults currently sleep in a monophasic pattern – that is, we try to take a long, single bout of slumber at night, the average duration of which is now less than seven hours.
  13. For many of us, midnight is usually the time we consider checking our email one last time – and we know what often happens in the protracted thereafter.
  14. Our circadian biology, and the insatiable early morning demands of a post-industrial way of life, denies us the sleep we vitally need.
  15. Should you ever have to give a presentation at work, for your own sake, and that of the conscious state of your listeners – if you an, avoid the midafternoon slot. This brief descent from high-degree wakefulness to low-level alertness reflects an innate drive to be asleep and napping in the afternoon.
  16. Sleep before learning refreshes our ability to initially make new memories. It does so each and every night. While we are awake, the brain is constantly acquiring and absorbing novel information (intentionally or otherwise).
  17. The term “muscle memory” is a misnomer. Muscles themselves have no such memory: a muscle that is not connected to a brain cannot perform any skilled actions, nor does a muscle store skilled routines. Muscle memory is, in fact, brain memory. Training and strengthening muscles can help you better execute a skilled memory routine. But the routine, itself – the memory program – resides firmly and exclusively within the brain.
  18. Daytime naps that contain sufficient numbers of sleep spindles also offer significant motor skill memory improvement, together with a restoring benefit on perceived energy and reduced muscle fatigue.
  19. You do not know how sleep-deprived you are when you are sleep-deprived.
  20. After sixteen hours of being awake, the brain begins to fail. Humans need more than seven hours of sleep each night to maintain cognitive performance. After 10 days of just seven hours of sleep, the brain is as dysfunctional as it would be after going without sleep for 24 hours.
  21. For everything thirty seconds you’ve been reading this book, there has been a car accident somewhere in the US caused by sleeplessness.
  22. Drowsy driving alone is worse than driving drunk. Drunk drivers are often late in braking, and late in making evasive maneuvers. But when you fall asleep or have a microsleep, you stop reacting altogether. There are no ” accidents” caused by fatigue, microsleeps, or falling asleep. They are crashes, as they are unnecessary and preventable.
  23. No matter what you may have heard or read in the popular media, there is no scientific evidence we have suggesting that a drug, a device, or any amount of psychological willpower can replace sleep.
  24. We have, however, discovered a very rare collection of individuals who appear to be able to survive on six hours of sleep and show minimum impairment – a sleepless elite. Part of the explanation appears to lie in their genetics, specifically a sub-variant of a gene called BHLHE41. The number of people who can survive on five hours of sleep or less without impairment expressed as a percent of the population and rounded to a whole number is zero. There is but a fraction of 1% of the population who are truly resilient to the effects of chronic sleep restriction at all levels of brain function.
  25. Depression and extreme negative mood can, for example, infuse an individual with a sense of worthlessness, together with ideas of questioning life’s value.
  26. Major depression has as much to do with the absence of positive emotions, a feature described as anhedonia: the inability to gain pleasure from normally pleasurable experiences such as food, socializing, or sex.
  27. Even the most elemental units of the learning process – the production of proteins that form the building blocks of memories within these synapses – are stunted by the state of sleep loss.
  28. Like a car engine that is revved to a shrieking extreme for sustained periods of time, your sympathetic nervous system is floored into perpetual overdrive by a lack of sleep. The consequential strain that is placed on your body by the persistent force of sympathetic activation will leak out in all manner of health issues, just like the failed pistons, gaskets, seals, and gnashing gears of an abused car engine.
  29. Sleep loss increases levels of circulating endocannabinoid, which, as you may have guessed from the name, are chemicals produced by the body that is very similar to the drug cannabis. Like marijuana use, these chemicals stimulate appetite and increase your desire to snack, otherwise known as having the munchies.
  30. Not sleeping enough, which for a portion of the population is a voluntary choice, significantly modifies your gene transcriptome – that is, the very essence of you, or at least you as defined biologically by your DNA. Neglect sleep and you are deciding to perform a genetic engineering manipulation on yourself each night, tampering with the nucleic alphabet that spells out your daily health story.
  31. Perhaps, it’s not time that heals all wounds, but rather time spent in dream sleep, offering emotional resolution when you awake the next morning.
  32. This was the theory of overnight therapy. The process of REM-sleep dreaming accomplishes two critical goals: 1) sleeping to remember the details of those value, salient experiences, integrating them with existing knowledge and putting them into autobiographical perspective, yet 2) sleeping to forget or dissolve the visceral, painful emotional charge that had previously been wrapped around those memories.
  33. In the good sleepers, the parts of the brain related to inciting emotions (amygdala) and those linked to memory retrospection (hippocampus) quickly ramped down in their levels of activity as they transitioned toward sleep, as did basic alertness regions in the brain stem. This was not the case for insomnia patients. Their emotion-generating regions and memory recollection centers all remained active. Insomnia patients could not disengage from a pattern of altering, worrisome, ruminative brain activity.
  34. Many individuals believe alcohol helps them fall asleep more easily or even offers sounder sleep throughout the night. But are resolutely untrue. Alcohol sedates you out of wakefulness, but it does not induce natural sleep. The electrical brainwave state you enter via alcohol is not that of natural sleep; rather, it is akin to a light form of anesthesia.
  35. The reason you sometimes notice yourself sticking your hands or feet out of your bedcovers when sleeping is because at night, due to your core becoming too hot, your body naturally wants to keep the body core cool, allowing you to fall and stay asleep, and this happens without you really realizing it.
  36. Sleeping pills do not provide natural sleep, can damage health, and increase the risk of life-threatening diseases.
  37. Sleep deprivation degrades many of the key faculties required for most forms of employment. Why, then, do we overvalue employees that undervalue sleep? We glorify the high-powered executive one mail until 1 am and then in the office by 5:45 am; we laud the airport “warrior” who has traveled through five different timezones on seven flights over the past eight days.
  38. Insufficient sleep robs most nations of more than 2% of their GDP – amounting to the entire cost of each country’s military. It’s almost as much as each country invests in education. Just think, if we eliminated the national sleep debt, we could almost double the GDP percentage that is devoted to the education of our children.
  39. The irony that employees miss is that when you are not getting enough sleep, you work less productively and thus need to work longer to accomplish a goal. This means you often must work longer and later into the evening, arrive home later, go to bed later, and need to wake up earlier, creating a negative feedback loop.
  40. The circadian rhythm of teenagers shifts forward dramatically by one to three hours. So really the question is if you are an adult: Could you concentrate and learn anything after having forcefully been woken up at 3:15 am day after day after day? Would you be in a cheerful mood? Would you find it easy to get along with your co-workers and conduct yourself with grace, tolerance, respect, and pleasant deamenour? Of course, not. Why, then, do we ask this of millions of teenagers and children in industrialized nations? Surely this is not an optimal design of education.
  41. Nicotine is also a stimulant often causing smokers to sleep only very lightly. In addition, smokers, often wake up too early in the morning because of nicotine withdrawal.
  42. 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. Then we may remember what it feels like to be truly awake during the day, infused with the very deepest plentitude of being.
When you were dreaming last night, you started to see things that were not there - you were hallucinating . You believed things that could not possibly be true - you were delusional . You became confused about time, place, and person - you were disoriented . You had extreme swings in your emotions - you were affectively labile. You woke up this morning and forgot most, if not all, of this bizarre dream experience - you were suffering from amnesia . If you were to experience any of these symptoms while awake you'd be seeking immediately psychological treatment.
*I take no credit for any of these points.

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