Here's my disclaimer... I am no professional anything except maybe slacker.
That said, I'd guess the what it is might be less important than why it is. You mentioned this happened during t time. I'm inclined to agree with what amandalouise mentioned... I have to wonder if something particularly stressful/upsetting/push-ish was going on when this happened. It might be as simple as going too fast with t and that was just how you reacted to whatever was going on. Stress can produce all kinds of responses in people. It's certainly worth talking with your t about, if for no other reason than maybe to find better ways to pace it out so you don't have to have this happen when talking to t. You're already working on things that cause fear responses (if I read right) the last thing you need in difficult times is more difficulties on top of that. Here's hoping this gets figured out for you with quickness.

-Avery