What is the body clock, and how does it decide when I'm sleepy?
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.
Topics
How sleep works
What the body and mind are doing through a night, from the first drift to the first light.
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02
How much sleep do I really need?
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.
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03
What happens while we 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.
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04
What is deep sleep, and am I getting enough?
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.
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05
What is 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.
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06
What makes us feel sleepy?
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.
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07
Why do we dream?
Why we dream, why dreams are so strange and borrow from yesterday, and what the main scientific theories say dreams are for.
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08
Why are some nights better than others?
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.