It sounds like a simple question: Why do we sleep?
But the answer is surprisingly complex. To many researchers, sleep is a bit of a mystery; we know that we need it to function, but we’re not sure why it’s totally necessary from an evolutionary perspective.
If you live a normal life, you’ll sleep for about a quarter of a century—25 full years. What’s happening to your body during all of that time?
1. First, your body temperature drops.
This occurs during the first stage of sleep. Your body temperature slowly drops, allowing you to access the deeper stages of sleep; if you’re in a cool room, the process is easier, which is why sleep experts sometimes recommend lowering your thermostat if you’re suffering from insomnia.
You’ll also gradually become disengaged from your surroundings. However, your breathing will remain normal until you reach the deeper stages of sleep.
2. You dream, and your brain might begin to practice different scenarios.
Some scientists believe that during rapid eye movement (REM) sleep, your brain runs through various situations in order to practice its responses. Unless you have a sleep disorder, your body is temporarily paralyzed while this occurs; you’re therefore allowed to dream without physically acting out those responses.
This isn’t a universally accepted theory, however. Some scientists believe that the brain uses REM to “reorganize” itself, discarding unnecessary memories to allow for most efficient functionality. In any case, you’ll dream about 3 to 5 times per night, although you won’t remember most of your dreams.
3. As you go into deeper sleep, you stop dreaming.
The deepest stages of sleep are restorative to your muscles and other tissues. At this point, your blood pressure drops significantly, and you breathe much more slowly. Your muscles benefit from increased blood flow, and they relax completely.
Your body also releases hormones to repair muscle tissue and promote growth. If you exercise, these sleep stages are absolutely vital, as without them, your body will be unable to effectively build new muscle.
4. The cycle resets.
While you might need that deep, restorative sleep more than light REM sleep, you won’t get it right away—your body cycles through the different stages of sleep, and you’ll spend the majority of your slumber in one of the lighter stages.
So, why doesn’t your body let you sleep deeply if that’s what you need? You may need to wake suddenly to respond to a threat, and because sleep induces a temporary paralysis at the deeper stages, your body wants to keep you relatively in the moment.
In the early hours of the morning, you’ll spend more and more time in the “lighter” stages of sleep. That’s why your alarm should wake you up fairly effectively—and why you’ll often wake up after a strange dream. REM sleep might also help you wake up, although researchers are still looking into that.
Most people should get about 7 to 8 hours of sleep per night, although this number can vary with your individual biology. The main takeaway, however, is clear: If you’re not getting enough sleep, your entire day suffers.
Make sure you’re able to wake up feeling rested and ready to go—otherwise, your head might need to hit the pillow a bit earlier.