Once towards the end of a session. I got too mad to stay. I told T that I had to go and she said ok and moved back a little. I left, went to my transition room (this was at the old clinic) and worked through my anger. I returned about 10 mins later, it was right at time or shortly after. I asked if we were ok and she said we were. I apologized for having to leave.
I had one other session that I didn't leave but I was so mad that I stopped talking like 10 mins into the session and didn't talk very much at all even though T kept trying to work with me. On that session, I was shaking so bad that I couldn't pack up my backpack to leave - I ended up sitting back down and talking for about 30 mins. I had asked her if she had the time to stay and she did.
Otherwise, if I got triggered, I would disassociate to some degree and was unable to leave.