Dreamland: Adventures in the Strange Science of Sleep has everything you ever wanted to know about sleep, including myths and truths, as well as the downright strange. Author David K. Randall shared five facts from his book.

Sleep wasn’t something we were supposed to worry about in the first years of the twenty-first century. There were bigger things that required attention: technology made the world smaller by the day, the global economy blurred the lines between one day and the next, and daily life was filled with questions over what was considered normal.

Most of us never give sleep much thought, and if we do, we tend to think of it as nothing more than an elegant on/off switch that our bodies flip when we need to take a break from our overscheduled life. Sure, we would like to get more of it, and yes, we have had had a weird dream or two lately, but beyond that, the importance of sleep likely hovers somewhere near that of flossing for most of us: something that we are supposed to do more often but don’t.

I once thought little of sleep; that is, until I started sleepwalking and ran myself into a wall in my apartment. My doctor’s disconcerting admission that science still doesn’t know much about sleep prompted me to investigate this mysterious third of life. I soon found that sleep underpins nearly every moment of our lives, affecting everything from how we raise our kids to how soldiers function on the battlefield to which teams come out ahead on Monday Night Football.

Here are five surprising things that you may not know about sleep.

1. Sleep is one of the youngest fields of science. Until the middle of the twentieth century, scientists thought that sleep was an unchanging condition during which time the brain was quiet. The discovery of rapid eye movement sleep in the 1950s upended that. Researchers soon realized that REM sleep is a time when the brain is as active as it is when a person is awake, and the time when most dreams occur. There are now over 75 recognized sleep disorders, and sleep scientists consider themselves in the golden age of their field.

2. A woman’s sleep quality can be a predictor of happiness in a marriage. Dr. Wendy Troxel, a professor of psychiatry at the University of Pittsburgh, recruited married subjects who agreed to wear a wristwatch sleep monitor for 10 days and then rate each of their interactions with their partners. The results were clear: the most severely negative ratings came after nights when the wife had slept poorly. Not only that, but the quality of wives’ sleep was a more important predictor of happy interactions than a hard day at work or any other form of stress. Men tend to sleep better next to their partners than when they go to bed alone, but that may be because they get to enjoy the emotional benefits of proximity without having to listen to their partners snoring. In one of nature’s dark jokes, women not only are far less likely to snore than men but also tend to be lighter sleepers. The result is a nightly farce that is one reason why wives also suffer from insomnia more often than their husbands.

3. Focusing on treating nightmares may help combat veterans readjust to civilian life. Since at least the Vietnam War, when more than one in five combat veterans returned home with chronic nightmares, drugs have been the main line of defense against a brain stuck in a cycle of bad dreams. But there may be a better way. Doctors currently think it is possible to train the brain to dream about other subjects, in a sense rewriting the stories that we tell ourselves each night. One promising technique is called imagery rehearsal therapy, in which a person first describes the traumatic event and then discusses an image to replace it. In one study, this form of therapy was as effective at reducing nightmares as medication.

4. It’s possible to kill someone while you are sleepwalking. In one famous case in Canada in the late 1980s, a man drove 14 miles to his in-laws house. He let himself in with his key, and then proceeded to stab his mother in law to death and nearly kill his father in law. Yet at the trial, doctors testified that there was a simple explanation why someone would suddenly choose to attack those he was close to: he was sleepwalking. The jurors agree and he was acquitted. A person who is sleepwalking is almost literally half-asleep: the eyes may be open and the body is able to perform complex maneuvers like driving, but the rational part of the brain isn’t what we would consider conscious. The question of whether a sleepwalking person who harms someone else should be culpable or is simply a bystander to an action the body performed unwillingly continues to plague the legal system. Deborah Denno, a professor at Fordham Law School, argues that the criminal code needs to be changed to recognize that some actions can be “semi-voluntary.”

5. Sleep affects the outcome of professional sports. All of us have a roughly 24-hour natural clock that guides our bodies that explains why we tend to wake up naturally around 9 a.m. and get sleepy around 2:30 p.m. Researchers have discovered that athletes performing at the peak of the circadian rhythm – or between about 6 p.m. and 9 p.m. – are able to lift slightly heavier weights, jump slightly farther, and have slightly quicker reaction times. This can have an outsized affect on professional football games. The NFL has the greatest parity among teams, meaning that the actions of one or two players can have a meaningful affect on the final scoreboard. One study by researchers at Stanford found that West Coast teams are at an advantage when squaring off against East Coast teams on Monday Night Football simply because their bodies are at an earlier stage in their circadian rhythm.