I have. Several times. It happens when it gets too intense and I feel I need a break.

The first time, she offered to come with me and I was pretty firm in saying "no". I went outside for some air and went back after 5 mins or so. It's happened quite a lot since and now T just lets me go when I say I need to leave. She knows I will come back. I sense by her reaction each time that she also regroups in the time that I am out of the room because she welcomes me back with a summary of where we were at. She's always been very kind about it.