tukareta node, sofa ni suwatte yasumimasu.

疲れた is the plain past form of 疲れる.

In this sentence, 疲れた does not just mean became tired in a strict past-time sense. Very often in Japanese, the past form of a verb like 疲れる is used to describe a current resulting state:

• 疲れた = I got tired / I’m tired

So 疲れたので means because I’m tired or because I got tired.

By contrast:

• 疲れます = polite non-past form, like get tired / will get tired / do get tired
• It would not fit naturally here as the reason for resting right now.

Both ので and から can mean because, but they feel a little different.

• ので sounds a bit softer, more explanatory, and often a little more neutral or polite.
• から can sound more direct or more like the speaker’s personal assertion.

So:

• 疲れたので、休みます。 = Because I’m tired, I’ll rest.
  Soft, natural, explanatory.
• 疲れたから、休みます。 = also correct, but a bit more direct.

For many learners, a simple rule is:

• Use ので for a gentler because
• Use から for a more straightforward because

This is completely normal in Japanese.

In subordinate clauses, Japanese often uses the plain form, even when the main sentence ends politely.

So this pattern is very common:

• plain form + ので／から
• polite form at the end of the sentence

Examples:

• 時間がないので、急ぎます。
• 雨が降っているので、行きません。

The politeness of the sentence is mainly shown at the end, with 休みます.

So 疲れたので、ソファに座って休みます。 is natural and grammatically normal.

The particle に is used with 座る because 座る is treated as movement into a position.

So:

• ソファに座る = sit on the sofa / sit down onto the sofa

Here, に marks the place that becomes the target of sitting.

Compare:

• 椅子に座る
• 床に座る
• ベンチに座る

All are standard.

Because 座る normally takes に, not で.

A useful way to think about it:

• に = destination / target position
• で = place where an action happens

Since 座る means to sit down or to take a seated position, Japanese usually uses に.

So:

• ソファに座る = correct
• ソファで座る = unnatural in most contexts

However, で would be natural with 休む by itself:

• ソファで休みます = I’ll rest on the sofa

In your sentence, though, the speaker is specifically saying:

1. sit on the sofa
2. rest

So ソファに座って休みます works well.

座って is the て-form of 座る.

The て-form has many uses, and here it links actions together. It can suggest:

• sequence: sit down and then rest
• accompanying state: rest while sitting
• a natural connection between the two actions

So 座って休みます means something like:

• sit down and rest
• rest sitting on the sofa

The て-form is extremely common for joining verbs like this.

It can feel like both, depending on context.

Literally, it is two verbs:

1. 座って = sit down / sit
2. 休みます = rest

But together, they naturally form one smooth idea:

• I’ll sit on the sofa and rest
• I’ll rest on the sofa, sitting down

Japanese often chains actions this way without sharply separating them.

It can suggest either, and in many everyday situations the difference is not important.

Because 疲れた is the past form of 疲れる, the literal idea is:

• I got tired

But in natural English translation, it often becomes:

• I’m tired

That is because the sentence focuses on the current condition resulting from becoming tired.

So a learner should understand 疲れたので as expressing the reason based on the speaker’s present state.

Yes, the subject is omitted, and that is very common in Japanese.

From context, the natural subject is:

• I am tired
• I will sit on the sofa and rest

Japanese often leaves out subjects when they are obvious.

So instead of saying:

• 私は疲れたので、私はソファに座って休みます。

Japanese normally says just:

• 疲れたので、ソファに座って休みます。

This sounds much more natural.

Yes, you could, but the nuance is slightly different.

• 疲れたので = because I got tired / because I’m tired
• 疲れているので = because I am in a tired state

Both can be natural.

Very roughly:

• 疲れたので is common and straightforward in everyday speech.
• 疲れているので can sound a little more explicitly focused on the ongoing state.

In many situations, either one would be understood just fine.

The comma helps separate the reason clause from the main action:

• 疲れたので、 = because I’m tired,
• ソファに座って休みます。 = I’ll sit on the sofa and rest.

Japanese commas are often used for readability and rhythm. In a short sentence like this, the comma is helpful but not absolutely required in every context.

So:

• 疲れたので、ソファに座って休みます。 = very natural
• 疲れたのでソファに座って休みます。 = also possible

No, standard Japanese normally does not use spaces like this.

Standard writing would be:

• 疲れたので、ソファに座って休みます。

Spaces are often added in teaching materials to make it easier for beginners to see the parts of the sentence.

So the spaced version is for learning, not normal native-style writing.

Yes. A native speaker might shorten or simplify it depending on the situation.

For example:

• 疲れたので、休みます。
• 疲れたから、ソファに座って休む。
• 疲れた。ソファで休む。

The original sentence is nice because it clearly shows both the reason and the action. It is natural and easy to understand, especially for learners.