简述：每天都离不开的睡眠，我们从碎片化的信息中了解一些，但或许是过于复杂的头绪和片面的信息接收，让我们在睡眠全貌上显得条理并不清晰，如我们入眠可以区分为几个阶段，每个阶段表现的生理特征是啥？我们的梦在哪个阶段？如果自己也混沌模糊，这篇科普可以助你解惑睡眠。
整理：2023年10月20日于昆明南站
Does Your Body Shut Down for Sleep?
你的身体会在睡眠中“关机”么？
来源: https://www.wonderopolis.org
Hey you! Wake up! Yes, we're talking to you. Now is not the time to sleep. It's time to wonder.
嘿！快醒醒！是的，我们在和你说话。现在不是睡觉的时候，是该感到好奇的时候了。
So what are we talking about today? You guessed it! Sleep. Sounds boring, right? After all, not much happens during sleep. Your body just kind of shuts down, doesn't it? Well, read on and you might be surprised to find out all that does happen when you sleep.
那么我们今天讨论的是什么呢？你猜对了！睡觉。听起来很无聊，对吧？毕竟，在睡觉时并不会发生太多的事情。你的身体就有点像是停止运转了，不是吗？那么，继续读下去，你可能会惊讶地发现所有在你睡觉的时候发生的事情。
So what exactly happens when you sleep? Does your body just shut down? Not at all! You actually go through five stages during sleep, and your brain guides your body along the way, telling it how to sleep.
那么当你睡觉的时候到底发生了什么呢？你的身体会停止运转吗？完全不会！实际上，你会在睡觉中经历了五个阶段，你的大脑一路引导你的身体，告诉它如何入睡。
In the first stage, your muscles relax, your body temperature gets a bit cooler, and your heart beats a bit slower.
在第一阶段，你的肌肉开始放松，体温变得有点凉一些，心跳也开始变慢。
In the next stage, you fall into a light sleep. At this point, you can still be awakened fairly easily.
在下一个阶段，你会进入浅层睡眠，这时，你仍然可以很容易地被唤醒。
As you enter the third stage, your body goes into a deeper sleep. Your blood pressure lowers, and your body becomes less sensitive to your environment. At this point, it's harder to awaken you.
当你进入第三阶段，你的身体进入更深层的睡眠。你的血压下降，身体对环境变得不那么敏感。这时候要唤醒你就会难一些了。
The fourth stage is an even deeper sleep. In this stage, it's difficult to wake you up. If you are awakened at this stage of sleep, you're likely to be really out of it and confused for a while.
第四阶段是更深层的睡眠。在这个阶段，是很难叫醒你的。如果你睡觉的时候，在这个阶段被唤醒，你很可能真的从睡眠中醒来并且困惑一段时间。
The final stage of sleep is known as REM sleep. REM stands for "rapid eye movement". During REM sleep, your body's muscles are totally relaxed, but your eyes move back and forth rapidly behind your eyelids. REM sleep is when most dreams occur.
睡觉的最后一个阶段被称为快速眼动睡眠。Rem 代表“快速眼动”。在快速眼动睡眠期间，你的身体肌肉完全放松，但你的眼睛在眼睑后面快速前后移动。做梦就大多发生在快速眼动睡眠期间。
Sometimes when you're falling asleep, your body may suddenly jerk and you're back awake for a second. Has that ever happened to you? Why does it happen?
有时候当你睡着的时候，你的身体会突然抽搐，然后你又清醒了一秒钟。你有过这样的经历吗？为什么会这样？
Scientists call those experiences sleep starts or hypnic or myoclonic jerks, and they're not sure exactly why they happen.
科学家们把这些经历称为睡眠惊跳或者入睡或肌阵挛性抽搐，他们也不确定这一现象发生的原因。
But they're very common and completely normal. Since they occur before you enter the deeper stages of sleep, some scientists believe they may be the brain's reaction to your body's muscles relaxing.
但这一现象非常普遍，而且完全正常。 因为它们发生在你进入深度睡眠之前，一些科学家认为它们可能是大脑对你身体肌肉放松的反应。
Sometimes your brain may interpret your relaxing muscles as falling and tense your muscles suddenly in response to prevent a fall, resulting in an involuntary body jerk.
有时你的大脑可能会把你放松的肌肉理解为你会跌倒，然后突然收紧你的肌肉，避免跌倒，从而导致无意识的身体痉挛。
