Questions & Answers about Я вздохнул и ничего не сказал.
Because it is a past tense verb.
In Russian, past tense is formed from the infinitive stem plus a form that agrees with gender and number:
- вздохнул = masculine singular
- вздохнула = feminine singular
- вздохнуло = neuter singular
- вздохнули = plural
So Я вздохнул means I sighed if the speaker is male. A female speaker would say Я вздохнула.
For the same reason: it is another past tense verb agreeing with the speaker.
Since the subject is я, Russian past tense still shows gender:
- Я сказал = I said (male speaker)
- Я сказала = I said (female speaker)
So the sentence as written sounds like it is spoken by a man.
Yes, Russian can often omit subject pronouns, especially when the meaning is clear from context.
So both of these are possible:
- Я вздохнул и ничего не сказал.
- Вздохнул и ничего не сказал.
Including я can make the subject more explicit, more contrastive, or simply more natural in that context. It is not always required, but it is perfectly normal.