What is sleep, and why do we have to sleep?

One of my friends posted something on Quora about sleep and I got inspired to write my first post on this sub.<br><br>So...<br><br>Sleep is a fundamental bodily function that we all need to regularly do in order to survive, right up there with eating and breathing. So why, from a scientific perspective, do humans need to sleep? Why do they need to rest their bodies for eight hours every night?<br><br>Well, first of all, humans need to do this because of a bodily function called a circadian rhythm. A circadian rhythm is basically a 24-hour body clock that all humans have. Your body will have a circadian rhythm in order to sort out what needs to be done at the right time in a day. This helps you respond to your environment and react to external conditions, such as light/dark, warmth, and cold. When your body’s internal clock says that it’s nighttime, it sends signals to your brain, and it tells you that it’s time for bed.<br><br>Now, as it turns out, humans don’t have an inner depot of energy that we can tap into as the day goes on. We have to drink and eat in order to keep our bodies functioning, and we need to do it multiple times a day. We do this partly so that we can sleep. When sleep, pretty much all of the functions in our body slow down. We don’t need as much energy, so our bodies don’t need to burn calories to fuel it. This is why we can survive a full night of no food or water, but we can’t do that for a full day.<br><br>This is all good, but why do we need to shut down in order to sleep? Why can’t we just lie in bed and burn calories like normal, sort of like how we slow down a little bit when we watch TV, but our bodies still burn calories to make sure we can blink, breathe, and move around freely. Why can’t we do that when we sleep?<br><br>The reason why it’s like this is because we, sort of, do burn calories while we sleep. We have something called our autonomic nervous system that sort of works like a car’s autopilot mode. It helps us function, but it doesn’t do it at 100%. This is why we can sleep. Our brains don’t need to run at 100% when we’re sleeping because we’re not doing anything, and it’s dark, and there’s nothing for it to do. So our brain, which does burn a lot of calories when it’s working full blast, is not working at 100%. It’s working at, let’s say, 40%.<br><br>Now, this is not true for when we’re dreaming, because in a way, our brains are simulating sort of real-life scenarios, where we have to run, dodge things, fight people, and other things that require pretty much 100% brain function. This is why some people wake up and are groggy and tired. Their brain goes from 40% straight to 100%, or God forbid, they woke up during a nightmare, and they were going at like 120%.<br><br>Now, this is all good, but why do we dream. This is the million-dollar question that pretty much everyone asking. Even science can’t really explain why we dream. The most popular explanation is that we dream when we sleep to process memories. This is why you can remember all the things you did from a very early age. Your brain is processing all of that data when you’re fast asleep, and that’s why you can remember it, and it’s also why sometimes you’ll see things from your childhood in your dreams. Your brain is processing memories, and sometimes it slips that into a dream that you have.<br><br>There are many other theories of why humans dream. Some say it’s a simulation from evolution, and we’re practicing real-life scenarios. Some say it’s just random chemical reactions inside our heads. We don’t really know why we dream, but we do know that it’s really really important. Many people who don’t dream, or don’t remember their dreams, are at a higher risk of getting diseases like Alzheimer’s disease, which is where pretty much your brain starts to slowly deteriorate and die. It’s not a very nice thing to happen, let me tell you.<br><br>So, to sum this all up, we need to sleep in order to conserve energy, we need to keep our brains working so we don’t forget anything, and we need to keep our brains healthy. Sleep is a vital part of the human functions, and I think a lot of us forget that, which is why some of us don’t get enough sleep. Thank God that’s not me.