Oh crap @Spiv1803 , these things always happen on a weekend.
Rescheduling is a pain, but never mind. If you are seeing a counselor, get an appointment with them first and have a chat about some coping strategies for when you get stressed. If you aren't seeing a counselor, start.
I use a very complicated breath counting exercise when I'm being subjected to any surgical or diagnostic monstrosity. It takes me out of the immediate situation and can keep me mentally busy for up to an hour. There are lots of different 'hack' to help you cope. And they do help--- I can do champion grade stressing and my little box of mental tricks has seen me through some shitty stuff. You just need to find the one that works for you. Marg xxx