Getting triggered happens all the time to me. I don't think that's questionable or anything, as long as you feel you have or are given tools to deal with it (i.e. general tips like how to calm yourself, but also things like being offered the possibility to get extra sessions if needed).

However, for a few weeks I was talking about my past a whole lot. Mainly due to the fact that I started to have flashbacks multiple times a day suddenly, unrelated to therapy. During that time, T asked me almost every session whether it was really okay to talk about this. He said that some people can't deal with talking about it this much and that it can then hurt to talk about it. But he always stressed that if I felt it helped me to talk about it and I felt I could do it, then it was fine.

So that's pretty much what I think of it now, if you feel you can deal with it somehow, and things overall don't get worse, then it's fine. Otherwise, I'd tell my T that maybe last session was a bit much and I needed to slow down a little, or just slow down on my own.