I have a similar thing happen although not at a trigger word and I hate it although after a couple of years I am getting better at managing it. It's wired isn't it. I think my t sees it as a form of regression as she used to ask how old I felt and when I can't talk tends to think it is pre verbal. I am not convinced but she is great at getting me to wiggle my toes and be aware of my senses and helps me to try and stay more present, but there have been times I have ended up sitting in the car not able to move for ages. I know just what you mean with the driving so I try to stay put until I am more with it if I can. If not she suggested I keep sweets with a strong flavour in the car and these and air and sometimes music help to bring me round so to speak
I was lucky that she generally notices what happens and has helped but sometimes I zone out too much to hear her and leaving is really difficult. It sounds like you are working on some tough stuff and part of you is finding it really difficult. Try and tell her if you can as I'm sure she's seen it before. See if she can help you with coping strategies as I think it is hard to stop it happening so managing it for me is the best bet.
Not sure if that is very helpful and hope you manage to find you own way. Will be thinking of you