# How sleep works

> What the body and mind are doing through a night, from the first drift to the first light.

- [How much sleep do I really need?](https://nitez.com/how-much-sleep): How many hours of sleep adults need, why it's a range rather than one number, and how to tell from your days whether you're getting enough.
- [What happens while we sleep?](https://nitez.com/stages-of-sleep): What happens while you sleep: light, deep and REM sleep, how the cycles repeat through the night, and why brief wakings are a normal part of it.
- [What is deep sleep, and am I getting enough?](https://nitez.com/deep-sleep): What deep sleep is, why it comes early in the night and thins with age, and why a tracker's deep sleep number is only a rough guess.
- [What is REM sleep?](https://nitez.com/rem-sleep): What REM sleep is, why your body can’t move while your brain is nearly awake, why it gathers toward morning, and what it may do for memory.
- [What is the body clock, and how does it decide when I'm sleepy?](https://nitez.com/body-clock): How your body clock works: a clock in nearly every cell, reset each morning by light, and why some people are simply built to sleep later.
- [What makes us feel sleepy?](https://nitez.com/sleep-pressure): Why sleepiness builds the longer you're awake, how the body clock puts it off, and why caffeine, naps and sleeping in work the way they do.
- [Why are some nights better than others?](https://nitez.com/good-nights): Why you sleep well one night and badly the next: how your day, wake time, light and hours awake shape tonight's sleep, and why some variation is normal.
- [Why do we dream?](https://nitez.com/why-we-dream): Why we dream, why dreams are so strange and borrow from yesterday, and what the main scientific theories say dreams are for.

https://nitez.com/topics/how-sleep-works