What does it mean to sleep well?

What happens while you sleep

What does it mean to sleep well? We spend almost a third of our lives asleep. And yet, it's the first thing we cut when we're short on time. What really happens while you sleep? In the next few minutes, you'll understand what your brain does at night, you'll work out what time to go to bed, and you'll walk away with a plan to sleep better starting tonight.

By the way, this is my house in MindHaOS, and this room, Rest, is where I keep my sleep schedule and the log of my nights. Let's get started.

Sleeping isn't switching off. During the night, you go through cycles of about ninety minutes, four to six a night, and each one takes you through several stages: light sleep, deep sleep and REM sleep, the stage of the most vivid dreams.

Deep sleep is most abundant early in the night. That's when your body releases growth hormone and repairs itself, and, according to studies in mice, when the brain works hardest at clearing out the waste it built up during the day.

REM sleep is concentrated toward the morning. That's when your brain is almost as active as when you're awake: it sorts through what you learned and processes the day's emotions. That's why, if you get up much earlier than you need to, you lose exactly that part.

What science has discovered about sleep

Before electric light, many people in Europe slept in two stretches: a first sleep, a while awake in the middle of the night, and a second sleep. The historian Roger Ekirch documented it in hundreds of diaries, letters and books from centuries past.

In 1879, Thomas Edison successfully tested his incandescent light bulb. The night filled with light, and over the years we went to bed later and later.

In 1938, the physiologist Nathaniel Kleitman spent thirty-two days inside Mammoth Cave, in Kentucky, to live on twenty-eight-hour days. His body wasn't fooled: it kept to a rhythm of about twenty-four.

In 1953, Kleitman and his student Eugene Aserinsky discovered REM sleep: they saw that, at certain moments of the night, the eyes move rapidly under the eyelids, and that people woken up at those moments were almost always dreaming.

And in 2017, the Nobel Prize in Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young, for discovering, in fruit flies, how the genes of the internal clock work. We'll get there.

How much sleep you need

Adults need seven hours or more each night, according to the American Academy of Sleep Medicine. Teenagers need eight to ten, and school-age children, nine to twelve. And yet, one in three adults sleeps less than seven.

Lack of sleep adds up. In a 2003 experiment, people who slept six hours a night for two weeks ended up with their attention as impaired as someone who had gone up to two nights without sleep. The worst part: they only felt a little tired.

Since sleep comes in cycles, waking up at the end of one feels better than waking up in the middle of deep sleep. Try it here: pick the time you get up, and the calculator tells you what times to go to bed, allowing about fifteen minutes to fall asleep.

And the best measure is you. If on vacation you wake up without an alarm at the same time as on weekdays, if you don't need coffee to get going, and you stay alert all afternoon, you're probably getting enough sleep.

Your internal clock

You have a master clock in your brain, the suprachiasmatic nucleus, which is set mainly by light. When it gets dark, you release melatonin, the hormone that tells your body it's nighttime.

That's why morning light is so powerful: getting a few minutes of sunlight soon after you wake up sets your clock and helps you feel sleepy at a good time at night.

Light at night does the opposite. In a 2015 study, reading on a tablet before bed delayed melatonin, made people take longer to fall asleep, and left them less alert the next morning than reading a paper book.

And not all of us have our clocks set to the same time: there are larks, who wake up early on their own, and night owls, who do better at night. Your chronotype depends largely on your genes and your age; it isn't laziness.

What you can control is regularity. A study of about sixty thousand people in the United Kingdom found that sleeping at consistent times is associated with lower mortality, even more than the number of hours. Staying up late on the weekend and getting up early on Monday is jet lag without leaving home.

How to prepare for a good night's sleep

Caffeine takes about five hours to drop by half. In one study, a strong dose taken six hours before bed cut more than an hour of sleep. See here how much is still in your body at bedtime.

Alcohol is deceptive: at first it makes you sleepy, but it fragments the second half of the night and reduces REM sleep. You sleep, but you don't rest as well.

Your bedroom matters too: cool, around eighteen degrees Celsius, or about sixty-five Fahrenheit, dark and quiet. And keep the bed for sleeping: if you work or watch shows in it, your brain stops linking it with sleep.

Plan the last hour of your day: put the screens away, dim the lights and do something relaxing, always the same, like reading, taking a warm bath or stretching. It's the signal to your body that night is coming.

I do it in Rest, my sleep room in MindHaOS: my schedule reminds me an hour before bed to put the screens away, and from the bedside lamp I open a guided breathing session to relax.

And move during the day: regular exercise helps you fall asleep sooner and sleep more deeply. Just finish your most intense workouts at least a couple of hours before bed.

When you can't sleep

If you've been lying awake for a good while, about twenty minutes, get up, go somewhere else with dim light, and go back to bed when you feel sleepy. Tossing and turning in bed teaches your brain that bed is for worrying.

Naps help if you keep them short and early: about twenty minutes, before mid-afternoon. In a NASA study with pilots, a nap of about twenty-six minutes improved their performance by thirty-four percent.

If insomnia lasts for weeks, the first treatment isn't sleeping pills: it's cognitive behavioral therapy for insomnia, which the American College of Physicians and the American Academy of Sleep Medicine recommend as the first option.

And if you want to know how you're doing, write down your nights for a couple of weeks: what time you went to bed, what time you woke up, and how you felt. The patterns show up on their own.

Remember that this guide is for information only. If you snore loudly and people tell you that you stop breathing, if you fall asleep during the day without meaning to, or if your insomnia won't go away, see a doctor: sleep apnea and other sleep disorders can be treated.

In short: sleep seven hours or more, at consistent times; get light in the morning and darkness at night; go easy on caffeine and alcohol; and plan the last hour of your day.

If you want to put it into practice the way I do, Rest, the sleep room in MindHaOS, has your sleep schedule with reminders and an alarm, a score for every night and the log of your nights, so you can see your patterns. The link is in the description, and you'll also find an interactive version of this guide there, so you can go over it at your own pace. In the next guide, we'll take on another question. See you then.