For me therapy is most certainly a trigger, but that's the whole point of it, and I need it. I'm the type of person who will not talk or think about my problems and I'll suppress it until I snap and have a breakdown. Even before the PTSD, if I was struggling with something, there's no way I would reach out to someone until I broke down right in front of them and had no choice. That's why I go to therapy. I can't break down and process what happened in my day to day life. It took me over a year to finally seek help, and on my first session, my therapist barely finished asking why I was there before I burst into tears.
I'm doing EMDR which has been very helpful, but it's exhausting, emotionally draining, and it does bring things back, that's the whole idea of it. For the rest of the day after one of my sessions, I'm a zombie. I can very rarely get any work done, I have very little interest in socializing, and most often I end up at home on my own reading or zoning out in front of the TV. The next day however, I usually start to think about what happened in therapy, and sometimes even that can be a trigger. But every time I feel like I resolve a tiny little bit more, or even just discover another part of it that I hadn't truly realized was affecting me.
I have two supporters. At first, no matter how difficult the therapy session was, no matter how much it affected me or made things difficult, I would always lie and tell them "Therapy is going great, I'm feeling much stronger! Everything is much better now." I'm sure they didn't really believe me, but they know me too well to try and push. Now I realize that that's just another way of avoiding, so now I say "It's hard. I feel awful after, but I know it's going to help." My therapy sessions involve reliving and making myself think of the most terrifying aspects of my trauma, so it is a trigger. But it's also allowing me an outlet where I CAN do that. It allows me to have more good days because I know I have a regular time and place to work through my issues. So it's awful, but in a helpful way. I don't know if that helps answer your question at all, but I hope it did a little.