Is your question why you didn't know who your therapist was?

If this is the case, it is likely that a new part has come out to meet T. This is actually a positive thing.

I have been with my T for a long time now so he knows all of me. But I do remember in the early days with him having the same thing happen as you. I sat through a whole session and at the end I had to ask who he was and his name, and write it down.

It's progress!