Depois da trovoada, eu não consegui voltar a adormecer.

Because da is the contraction of de + a.

• depois de = after
• a trovoada = the thunderstorm

So:

• depois de a trovoada → depois da trovoada

This kind of contraction is very common in Portuguese:

• de + o = do
• de + a = da
• em + a = na
• a + a = à

Trovoada usually means thunderstorm rather than just a general storm.

It comes from trovão = thunder. So trovoada suggests a storm with thunder, and often lightning too.

Depending on context, English translations might be:

• thunderstorm
• storm
• the storm

But thunderstorm is the most precise choice.

Yes — in Portuguese, the subject pronoun is often omitted because the verb ending already shows who the subject is.

So these both work:

• Depois da trovoada, eu não consegui voltar a adormecer.
• Depois da trovoada, não consegui voltar a adormecer.

Including eu can add:

• emphasis
• contrast
• clarity

In this sentence, eu is not required, but it is perfectly natural.

This is a tense choice.

consegui is the preterite of conseguir and refers to a completed event in the past:

• I didn’t manage to fall asleep again.

It presents the situation as a whole, as a finished fact.

conseguia is the imperfect and would suggest something more ongoing, habitual, or descriptive:

• I wasn’t able to... / I couldn’t... in a more background or repeated sense

Here, não consegui is the natural choice because the speaker is talking about one specific occasion after the thunderstorm.

Conseguir + infinitive means to manage to do something or to succeed in doing something.

So:

• consegui voltar a adormecer = I managed to fall asleep again
• não consegui voltar a adormecer = I didn’t manage to fall asleep again

This structure is very common:

• Consegui terminar o trabalho. = I managed to finish the work.
• Não conseguimos entrar. = We couldn’t get in.

Voltar a + infinitive means to do something again.

So:

• voltar a adormecer = to fall asleep again
• literally: to return to falling asleep

Other examples:

• Voltei a ler o livro. = I started reading the book again.
• Ela voltou a chover. would be wrong, because here you need the correct subject; instead: Começou a chover outra vez or Voltou a chover = It started raining again / It rained again

A very common equivalent is outra vez or de novo, but voltar a + infinitive is extremely natural in Portuguese.

This is a very important distinction.

• dormir = to sleep
• adormecer = to fall asleep

In this sentence, the speaker was already awake after the thunderstorm and is talking about the act of getting to sleep again. So adormecer is the right verb.

Compare:

• Não consegui dormir. = I couldn’t sleep.
  This can mean I was unable to sleep in general.
• Não consegui adormecer. = I couldn’t fall asleep.
  This focuses on the moment of entering sleep.
• Não consegui voltar a adormecer. = I couldn’t fall asleep again.
  This shows the person had been asleep before, woke up, and then couldn’t drift off again.

Because the first a belongs to the expression voltar a + infinitive, and the second a is simply the first letter of adormecer.

So:

• voltar a
  • adormecer

There is no contraction here. It stays a adormecer in writing.

This can look strange to English speakers, but it is normal in Portuguese. You may also see similar sequences like:

• começar a andar
• aprender a আঁ no, not that one
• voltar a abrir

In speech, the two vowels may flow together smoothly, but in writing they remain separate.

Yes, you might hear voltar a dormir, but the nuance is a little different.

• voltar a adormecer = to fall asleep again
• voltar a dormir = to go back to sleeping / to sleep again

In many real situations, both can work. But adormecer is more precise if you want to focus on the difficulty of actually drifting off again.

So this sentence is very natural because it emphasizes that the speaker woke up and could not get back into sleep.

Yes. In Portuguese, não normally comes before the conjugated verb.

So:

• eu não consegui... = correct

Not:

• eu consegui não voltar... unless you mean something different

These two are not the same:

• Eu não consegui voltar a adormecer. = I didn’t manage to fall asleep again.
• Eu consegui não voltar a adormecer. = I managed not to fall asleep again.

So the placement of não changes the meaning.

Yes, often it can.

• Depois da trovoada eu não consegui voltar a adormecer.
• Depois da trovoada, eu não consegui voltar a adormecer.

Both are understandable. The comma reflects a pause after the introductory time phrase Depois da trovoada.

In careful writing, the comma is very natural here, but in informal writing people may leave it out.

Usually it means after the thunderstorm, in a general time sense. In real use, it often implies after it had happened / after it woke me up / after it passed, depending on context.

It does not have to mean only the exact moment after the storm completely ended. It simply sets the time frame for what happened next.

If you wanted to be more explicit, you could say things like:

• Depois de a trovoada passar... = After the thunderstorm passed...
• Depois da trovoada me acordar... = After the thunderstorm woke me up...

But the original sentence is perfectly natural and idiomatic.

It works in both, but it sounds especially natural in European Portuguese.

A Brazilian speaker would also understand it easily, but in Brazil you might more often hear alternatives like:

• Depois da tempestade, eu não consegui voltar a dormir.
• Depois da trovoada, eu não consegui dormir de novo.

That said, trovoada, conseguir, and voltar a adormecer are all perfectly valid Portuguese. The original sentence fits very well with Portugal Portuguese style.

A more literal breakdown would be:

• Depois da trovoada = After the thunderstorm
• eu não consegui = I did not manage
• voltar a adormecer = to fall asleep again

So, literally:

• After the thunderstorm, I did not manage to fall asleep again.

That is a very close and accurate translation, even if natural English might sometimes prefer:

• After the thunderstorm, I couldn’t get back to sleep.

Both capture the idea well.