I have actually gotten in an accident after therapy... errr.... twice. One was very minor, the other not so much. The other one had significant contributing factors. there was a severe snow/ice storm and I was in a great deal of pain and had stopped taking my pain meds so I could drive. However, I was in so much pain I was in no condition to be driving by the time I left therapy. Add after effects of therapy and the storm and I feel fortunate it wasn't worse.
After that, my therapist really slowed our therapy down for a while. we also try to spend the last 10 minutes on lighter stuff. When I'm still dissociated after therapy I will walk around for a while. Then, depending on how I am, I will either take the very short drive to the library and hang out there or go some place and eat lunch or drive home. It's a long drive for me to get to and from therapy so cabs/uber aren't an option. And once, when it was really bad, she let me hang out in a separate area from the waiting room, with a blankie and a stuffie until I was ok