It's hypervigilance. Not just your mind, but your body is so used to being on alert for the next high-stress situation. My previous therapist told me I need to self-soothe mentally (tell yourself there is no danger, watch a calming video, listen to some nice music) and physically (figure out what part of your body is reacting and soothe it, so this might include stroking your chest, hugging a pillow, curling your toes).
I am terrible at this, but maybe it will work for you.
I used to encounter the same situation too, until I decide to start setting some boundaries and cut those people out of my life. Whenever I'm interacting with people these days, I'll compare the way they treat me vs the way I treat them. If I treat someone with kindness but they decide to repay me back with cruelty, then they will have to get out of my life.