Sleep Cycles and Your Body
Scientists are still figuring out exactly why humans need sleep, but they’ve figured out a lot about how it happens. All night long, your body and brain cycle through several different kinds of sleep.
Stage 1, or “light sleep,” happens right as you drift off. It lasts only 5–10 minutes. If you wake up now, you may feel like you haven’t slept at all.
Brain waves slow down.
Heart rate goes down, possibly so your heart muscle can rest. Blood pressure lowers, too.
Breathing slows to a regular, even pattern.
Muscles relax, aside from some occasional twitches that can make you feel like you’re falling (and sometimes jerk you awake)
Up to 70% of people have involuntary muscle twitches, called hypnic jerks, when falling asleep.
"Each night, when I go to sleep, I die. And the next morning, when I wake up, I am reborn.”
You spend most of a night’s sleep in this stage. You’re still in “light sleep,” but you become less aware of the world around you.
Heart and breathing rates go down even more.
Muscles get more relaxed.
Eye movements stop.
Body temperature starts to drop.
Your brain waves are still moving slowly, but with short bursts of activity called sleep spindles. Experts think these may be tied to how your brain stores memories.
Just after you learn a new task, you’re likely to have more sleep spindles during sleep.
"Sleep is a lovely hint of oblivion."