I think that's the PTSD. One element of an event that can contribute to its being traumatizing is surprise. We think one thing is going to happen and then out of the blue this other thing does. And the surprise/shock of that moment somehow helps embed the memory in a place it won't budge from. Then fast forward to present day and a surprise element can be triggering on its own. I too can get very scared and stressed when a negative thing surprises me. Someone being angry at me "out of the blue" would be much harder for me to handle than some just being angry at me. I would be scared and stressed out too. My T tries to do EMDR on this sort of thing (negative "surprise" experiences from childhood that got stuck).

Before my marriage broke up, there were many times I would not understand why my XH would suddenly be angry. We would be talking about something innocuous it seemed to me, and he would get mad and not say why. Towards the end I got braver and asked a couple of times why he was angry at me? What did I do? What did I say? I really did not know. And he would yell at me, "I am not angry at you!!" and I would cower. If he's not angry, why is he yelling at me? If he was really telling the truth and he was not angry, maybe it is a lesson for me that people can yell at you and look tense and have dagger eyes but not really be angry? I don't know. Maybe your H is not really mad at you, treehouse, but just acting in a way that you interpret as mad? I guess the best thing is to ask him, but I can see that would be scary too with the current atmosphere in the house.

I hope you are able to talk with your T before your session.