How to know if ～たら is hypothetical or temporal

Question

I encountered the following sentence in the chapter introducing conditionals from the online grammar guide Imabi.

休んだら、元気になった
When I rested, I got better.

Earlier, the article explained that たら can have either a hypothetical or a temporal meaning. When the verb in the main clause is in the non-past form, this is not an issue since the たら verb hasn't happened yet either way. To illustrate my meaning, take the following.

帰ったら、食べる。
When I go home, I'll eat. OR If I go home, I'll eat.

Regardless of which one is correct (most likely the first one), the action of "go home" has not yet happened.

However, in the case when the main verb is in the past (た形), I'm wondering if whether or not the conditional verb happened is clear or not. In other words, is the following translation possible?

休んだら、元気になった
If I had rested, I would have gotten better.

If not, how could the type of conditional above be translated?

And

If the main clause had a different subject than the conditional clause, would anything in the answer change? I'm only asking this because I have a feeling that a sentence like 「本を読んであげたら、弟が喜びました」where the speaker would be speculating about someone other than himself would change things (ignore this if it is too unclear).

Source: Imabi - 第109課: Conditionals I: The Particles と, なら(ば), たら, & ば

Answer 1

「休んだら、元気になった。」
「本を読んであげたら、弟が喜びました。」

I would interpret them as...

"When I rested, I got better."
"When I read a book for my little brother, he was delighted."

(In these examples, the たら verb happened and caused the main verb)

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If I wanted to say:

"If I had rested, I would have gotten better."
"If I had read a book for my little brother, he would have been delighted."

I would say like...

「休んだら(or休んでいたら)、元気になったのに / なっただろうに / なっただろう（なあ） / なっただろうけど。 etc...」
「本を読んであげたら(orあげていたら)、弟が喜んだのに / 喜んだでしょうに / 喜んだでしょう / 喜んだでしょうけど。 etc...」

(In these examples, the たら has a hypothetical meaning)

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_{In the examples below, the たら verb has not yet happened:}

_{「休んだら元気になるよ / 元気になるだろう。」
If you rest, you will get better.
「本を読んであげたら、弟が喜びますよ / 喜ぶでしょう。」
If you read a book for your little brother, he will be delighted.}

Answer 2

The past conditional usage that you are attempting assumes that the desired result did not occur. This is referred to as counterfactual conditional. This requires that both the condition and the result be conjugated correctly. If A, then B (would have happened). For this reason you should use a form that indicates condition in the latter part of your sentence as well as a certainty modifier like もし.

In your sentence 「本を読んであげたら、弟が喜びました」, the tenses do not match. 'If you read (present tense form) him a book, he was happy (past tense).

「元気になった」 and 「弟が喜びました」are simple statements (statements of fact). Change them to past-presumptive forms and you have a winner.

Some common usages:

「もし休んだら、元気になっていたでしょう。」

「もし弟に本を読んであげてたら、喜んでいたでしょう。」

Other possibilities:

「元気になれたでしょう」

「喜ばれたでしょう」