Group sessions tend to not work well, because people aren't generally comfortable treating this sort of thing as a valid trigger. So I tend to end up in situations where I just get it set off repeatedly. Because people tend in general to think that pushing therapy is good and harmless, even if I say it is a trigger for me.
And the fundamental trigger for me is the power imbalance. The situation where the professional could say that I said or did anything and be treated as reliable. Whereas me trying to defend or protect myself is taken as a sign that I'm clearly too sick and need to be forced back to treatment (with the same person causing the problem).
And I don't trust all the reports that say this doesn't happen or isn't common. Because as far as any official statistics go, what happened to me and other students didn't happen. And people who tell me that there's nothing to worry about tend to turn around and say I must be wrong about what I remember happening.