Hi! I'm sorry you are so triggered.
While our T want us to share what we are thinking with them, I also believe that they want us to feel comfortable with them. If you are not ready to go into all of the details at this point that is okay. As you feel safer, trust more and have more coping skills you may be able to go into more details. Your T should know that you wont necessarily be able to tell him all the details the first time you talk about it. And maybe not the second or third etc. If your T is open to you contacting him between sessions then you should. You should let him know what a hard time you are having. If you can't contact him between sessions, you should definitely bring your reaction up next session. You should not need to self medicate because of a therapy session.
Please take care and be gentle with yourself.