Breakdown of Она дотренировалась и потеряла сознание в зале.
и
and
она
she / it (for a feminine noun)
в
in / to (direction)
потерять
to lose (perfective)
Questions & Answers about Она дотренировалась и потеряла сознание в зале.
How exactly does the combination of до- and -ся change the meaning of the base verb here?
The combination (or circumfix) до- ... -ся shows that an action was carried out to an extreme limit, usually resulting in a negative consequence. Instead of just finishing her workout, she trained until she hit a physical breaking point.
Could I just say Она тренировалась и потеряла сознание instead?
You could, but you would lose the cause-and-effect emphasis. Using the imperfective тренировалась just means she fainted while she was training. The form дотренировалась explicitly tells us that the excessive training is exactly why she fainted.
Why use perfective verbs (дотренировалась and потеряла) here instead of imperfective ones?
They are perfective because they describe a sequence of completed actions with a final result. She completed the action of training to the limit, and then, as a direct sequential consequence, she lost consciousness.
Does в зале always mean 'in the hall'?
Literally yes, but context heavily changes its English translation. In the context of working out, зал is almost always short for тренажёрный зал (gym or fitness center) or спортивный зал (sports hall). So here, understanding it as 'gym' is much more natural.