I'm not amused by other peoples pain especially when I've been in an exact same scenario myself.

My t would often wait for me to start. One time we sat in silence for 40mins before I did what you did and left.

We had discussed this might happen at some point so she was prepared for my ways of coping. The only thing she ever said to me was that if I walk out, she still expects me to be at my next appt.

I have an idea of the pain you are in. Try and ground yourself as tree suggested. It will pass.

My heart goes out to you