Learn Hardcore Chinese: nǐ kuài xiūxi yíxià ba. - Hurry and take a rest for a bit.

So yes, the basic meaning of 快 is fast, but in this position it works more like an imperative adverb: “quickly / hurry and …”, not describing how you rest, but when you start resting (i.e., soon / now).

Why do we say 休息一下 (xiūxi yíxià) instead of just 休息?

一下 is very common after verbs in spoken Chinese. Here’s what it does in 休息一下:

It makes the action sound:
- Short / brief: rest for a bit, rest for a moment
- Light / casual / polite: not a heavy command.
It softens the tone:
- 休息！ alone can sound like a strong order: Rest!
- 休息一下。 feels lighter and more natural: Have a bit of a rest.

General pattern:

Verb + 一下: do the action briefly or in a low-pressure way.
- 看一下 – take a quick look
- 想一下 – think about it a bit
- 试一下 – try it (a bit)

So 你快休息一下吧。 feels like:
You, hurry and rest a little / go have a bit of a rest.

What exactly is the function of the particle 吧 (ba) at the end?

吧 is a sentence-final particle that, in this sentence, makes the sentence sound like a soft suggestion rather than a blunt command.

Compare:

你休息一下。 – You rest a bit. (can sound like a direct instruction)
你休息一下吧。 – You should rest a bit. (suggestion, softer, more caring)

Here, 吧:

Softens the mood
Expresses: I’m suggesting this / I think it’s a good idea for you

You’ll often see 吧 at the end of:

Suggestions: 我们走吧。 – Let’s go.
Invitations: 喝杯茶吧。 – Have a cup of tea.
Gentle commands: 别说话了吧。 – Don’t talk anymore, ok?

So 你快休息一下吧。 is like:
Come on, you should go take a rest now, ok?

Is 休息 (xiūxi) a verb or a noun in this sentence?

In 你快休息一下吧, 休息 is functioning as a verb: to rest.

你 – you
快 – quickly / hurry and
休息 – rest (verb)
一下 – a bit, briefly (verb complement)
吧 – suggestion particle

So the core is 休息一下 → rest a bit.

However, 休息 can also be a noun in other contexts:

休息时间 – rest time / break time
我需要休息。 – I need rest. (here it’s more like a noun)

You decide whether it’s verb or noun mainly by its position and what’s around it. In this sentence, because it follows 快 and takes 一下 as a complement, it’s clearly a verb.

Can I change the word order and say 快你休息一下吧 or 你休息快一下吧?

No, those word orders are not natural.

The basic pattern here is:

Subject + 快 + Verb + 一下 + 吧
→ 你快休息一下吧。

Details:

快 goes before the verb it modifies: 快休息, 快走, 快吃.
一下 goes after the verb as a complement: 休息一下, 看一下, 试一下.
吧 goes at the very end of the sentence.

So:

✅ 你快休息一下吧。 – correct
❌ 快你休息一下吧。 – unnatural
❌ 你休息快一下吧。 – wrong position for 快

Stick to the order: 你 + 快 + 休息 + 一下 + 吧.

Is this sentence polite or could it sound rude/bossy?

你快休息一下吧。 is generally caring and concerned, but it can also sound a bit insistent or urgent.

Common situations:

Someone looks very tired → you say it out of concern
A parent speaking to a child
Friends/colleagues speaking casually

Level of force:

It’s softer than a pure command like 你必须休息。 (You must rest.)
But stronger than a very neutral suggestion like 你可以休息一下。 (You can rest a bit.)

If you want to sound more polite/formal (to a superior, older person, customer, etc.), you might say:

您休息一下吧。 – Please rest a bit. (uses polite 您)
您要不要先休息一下？ – Would you like to rest first?

So in everyday context, 你快休息一下吧。 usually comes across as warm and worried, not rude.

Can I drop 你 and just say 快休息一下吧?

Yes, you can say 快休息一下吧。 and it will still be natural.

Dropping 你:

Makes it sound a bit more like a general command/suggestion to whoever is listening, or to a group.
Is very common in speech when it’s obvious who you’re talking to.

Examples:

Speaking directly to someone tired:
- 快休息一下吧。 – Hurry and rest a bit.
To a group of workers after a long task:
- 大家快休息一下吧。 – Everyone, hurry and take a break.

Keeping 你 makes it slightly more personal/pointed: you in particular should rest.

What’s the difference between 你快休息一下吧 and 你应该休息一下?

Both suggest that the person should rest, but the feeling is different.

你快休息一下吧。

Urgency + suggestion: Hurry up and rest a bit now.
Shows concern plus a push to act now.
More emotional, more spoken.

你应该休息一下。

Literally: You should rest a bit.
More objective or reason-based: it’s the right thing for you to do.
Can be neutral, but also slightly lecturing depending on tone.

Very rough English feel:

你快休息一下吧。 → Come on, go have a rest now.
你应该休息一下。 → You ought to rest a bit. / You should rest.

You can even combine them:

你应该休息一下，快休息一下吧。 – You should rest; hurry and rest a bit.

How is 一下 (yíxià) pronounced here, and why is it yí and not yī?

The characters are 一 (yī) and 下 (xià).

In isolation, 一 is yī (first tone).
But before another fourth-tone syllable like 下 (xià), 一 usually changes to second tone: yí.

So:

Written pinyin: yīxià
Actual spoken: yíxià (2nd + 4th tone)

This is a regular tone sandhi rule:

一
- 4th tone → pronounced as 2nd tone
  - 一半 → yíbàn
  - 一块儿 → yíkuàir

So 休息一下 is spoken as: xiūxi yíxià.

What’s the difference between 休息一下 and 休息休息?

Both Verb + 一下 and Verb + Verb (reduplication) can mean “do it a bit / briefly,” and they can often be interchangeable, but there is a small nuance.

休息一下

Very common, neutral way to say “rest a bit.”
Focuses slightly on the short duration or lightness of the action.

休息休息

Verb reduplication also softens the action and can feel a bit more casual or colloquial.
Feels like: rest a little, just rest a bit.

In this exact sentence, you can say:

你快休息一下吧。 – Very natural.
你快休息休息吧。 – Also natural, maybe slightly more informal in feel.

In most everyday contexts, they’re very close in meaning; both are fine.

Are there other common ways to say the same thing as 你快休息一下吧?

Yes, several very common variants express a similar idea:

你休息一下吧。
– Drop 快; still a gentle suggestion: Why don’t you rest a bit.
你快点休息吧。 / 你快点儿休息吧。
– 快点(儿) is like “a bit faster / hurry up”: Hurry up and rest.
你去休息一下吧。
– Adds 去 (go): Go (and) have a rest.
你先休息一下吧。
– 先 = first: Rest a bit first.

All of these are natural. The original:

你快休息一下吧。

combines urgency (快), a light tone (一下), and a soft suggestion (吧), giving a warm, slightly insistent:
You really should go rest a bit now.