Are you familiar with Subjective Units of Distress (SUDS)? This scale provides a quick way to let T know your level of distress during a session. Here is a version, from wikipedia:

10 = Feels unbearably bad, beside yourself, out of control as in a nervous breakdown, overwhelmed, at the end of your rope. You may feel so upset that you don't want to talk because you can't imagine how anyone could possibly understand your agitation.
9 = Feeling desperate. What most people call a 10 is actually a 9. Feeling extremely freaked out to the point that it almost feels unbearable and you are getting scared of what you might do. Feeling very, very bad, losing control of your emotions.
8 = Freaking out. The beginning of alienation.
7 = Starting to freak out, on the edge of some definitely bad feelings. You can maintain control with difficulty.
6 = Feeling bad to the point that you begin to think something ought to be done about the way you feel.
5 = Moderately upset, uncomfortable. Unpleasant feelings are still manageable with some effort.
4 = Somewhat upset to the point that you cannot easily ignore an unpleasant thought. You can handle it OK but don't feel good.
3 = Mildly upset. Worried, bothered to the point that you notice it.
2 = A little bit upset, but not noticeable unless you took care to pay attention to your feelings and then realize, "yes" there is something bothering me.
1 = No acute distress and feeling basically good. If you took special effort you might feel something unpleasant but not much.
0 = Peace, serenity, total relief. No more anxiety of any kind about any particular issue.