It sounds like you disassociated during therapy, the losing track of time happens when dissoasociation is taking place. You may have just been heading for a part of your past that your brain is worried about getting too upset about. I have experienced this myself, yes it is troubling and you should tell the therapist about how you felt.

Trama can get storred in parts of the brain that has no language either, maybe just sounds or pictures or feelings but no vocabulary. You might have to work at this from a different approach until you can get the words together to help you with addressing whatever is there.

I had that happen in a deposition, I was asked a question and could not talk, however I did have pictures, but now words. I was disoriented too for a while and just wanted to get home.

Don't get all upset, give it time and maybe something will come forward that you can begin to put words to a little at a time.

(((Hugs)))
Open Eyes