SOOOO interesting you ask this. I see my T about once a week. Last week and this week I've got stuff to tell her I'm nervous about. So, yes, I completely rehearse in my head pretending we're having the conversation. Interestingly enough, I think of her questions and it has helped me process things and figure things out. I'll have little "ah hah" moments. The day of I try not to think about it at all so the conversation will flow better and I won't get in there and blirt it all out as if I've memorized my lines.