Now, it's time for Words and Their Stories, a program from VOA Learning English that explores common expressions we use every day.

Sleep. It's important to our mental and physical health. From a quick cat nap to long, deep beauty sleep, we have many expressions to describe sleep.

Of course, cats sleep for many hours during the day. That's why we call a short period of sleep – preferably in a warm spot of the room – a cat nap.

The purpose of a cat nap is different from that of a power nap. We take power naps during the middle of a workday to help us get more work done. But we take a cat nap because the sun feels so good and our pillow feels so soft that we simply must close our eyes for a few minutes – like a cat.

If you had a really tough week at work, you might want to sleep in on the weekend. This means you sleep later than usual. Teenagers are especially known for sleeping in when they don't have school.

It's not hard to understand where we get some of our sleep expressions. For example, when we're tired, we may say we need to get some shut-eye. You can only sleep when you shut your eyes. Although, I have heard stories about people who sleep with their eyes open – which can look kind of creepy.

When we use this expression, please note that it is singular. We just say "shut-eye" and not "shut-eyes."

If you are feeling tired, you might need to catch some z's. "Z" is the sound we use to represent sleeping. So, to catch some z's simply means to sleep.

Now, sometimes we fall asleep when we don't mean to. We might nod off while sitting somewhere and waiting, like in a doctor's office or on the train after a long day of work. A "nod" is the up and down movement of the head. That head movement is what happens when you nod off while sitting. Your head drops down and ... you fall ... asleep.

Now, we might take a short snooze during the day to get a little rest. And if we had a late night, we might need to hit the snooze alarm or snooze button a couple of times before actually getting up. This lets us get a little more shut-eye.

Most of these expressions are for the short rests we take during the day -- but not when we actually go to bed at night. We have a whole different set of other expressions just for that!

You can simply turn in. This just means to go to bed for the night. When you fold down the blankets to get into bed, you are "turning down the bed."

Some people are just too tired to fuss with turning down blankets. They might say, "It's late. I'm going to crash." This means they are so tired that they feel like they need to fall -- or crash -- onto the bed. Young people are fond of this expression.

If you hit the sack or hit the hay you are officially going to bed for the night. A sack is a big bag, like the bag that rice comes in. Word historians say that in earlier days, people would fill empty rice sacks with something soft, like feathers, and make it a pillow.

And hay is the kind of dried grass that farmers put down for some farm animals to sleep on. It's actually quite comfortable. In fact, a long time ago, some beds were filled with hay.

Maybe you are one of those lucky people who drift off to sleep quickly. As soon as your head hits the pillow, you are out like a light. This means you fell asleep in the time it takes to turn off the light.

For some other people, sleep might not come so fast.

Some people might need to listen to peaceful music or read a book to help them fall asleep. Others might need to count sheep. When you count sheep, you imagine cute little sheep jumping over a fence. The scene is so relaxing -- and counting sheep is so boring -- that will you soon be sawing logs. That is to say, you are so deeply asleep that you will start snoring loudly.

Some people may fall asleep quickly, but then they have a restless night's sleep. They toss and turn all night. And what about those times when you can't seem to fall sleep at all? For those nights you can say, "I didn't sleep a wink!"

Now, a couple of expressions with the word "sleep" aren't actually about sleep at all.

Sometimes when we have something on our mind that is important to us, we might think about it as we're falling asleep. It might keep us awake. On the other hand, if there is an issue that you simply don't care about at all, you can say that you are not going to lose any sleep over it.

We often use this to answer something said to us.

Here's an example:

A: Wow. Curtis is really mad at you. He said he's not going to forget what you did at the party last night.

B: I didn't do anything. And anyway, Curtis is all talk. Trust me. I'm not going to lose any sleep over his empty threats.

Now, if you want someone to spend more time thinking about something, you can tell them to sleep on it. We usually say this when someone has to make a decision.

Let's hear how to use this expression. In this short conversation, one person wants to get away for some R&R, also known as "rest and relaxation." The other doesn't feel so free.

A: Okay, so here's the plan. If we leave straight from work on Friday and drive to the cabin, we should get there by 11. That gives us all day Saturday, Sunday and Monday to ski or hike in the mountains. We can head home Monday night.

B: I'm not sure if I can miss work on Monday.

A: But it's a holiday. Don't you need some R&R?

B: I do. But I also need to work on a big project. I think I'll actually feel more rested and relaxed if I work on it.

A: Look, you don't have to make up your mind right now. Sleep on it and let me know by Thursday if you can go.

And that brings us to the end of this Words and Their Stories. This is Anna Matteo hoping that tonight you sleep like a log! And as we like to say to our children: "Sleep tight. Don't let the bed bugs bite!"

In the Comments Section, please share some of your sleep expressions.

Anna Matteo wrote this story for VOA Learning English. Ashley Thompson was the editor.

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pillow – n. a bag filled with soft material that is used as a cushion usually for the head of a person who is lying down

fold – v. to bend one part of something over or against another part

blanket – n. a covering made of cloth that is used especially on a bed to keep you warm

fuss – v. activity or excitement that is unusual and that often is not wanted or necessary

drift – v. to change slowly from one state or condition to another : "drift off to sleep"

relaxing – adj. helping you to rest and to feel less tense, worried, nervous, etc.

snore – v. to breathe noisily while sleeping

restless – adj. having little or no rest or sleep

all talk - idiom talking about doing things but never actually doing them

empty threat – n. a threat that someone does not really mean