I have only just seen this post, I'm no expert at all but I also had a brain trauma last year, a severe concussion.
Several months later I started "missing time", I could be walking along and it felt as though I suddenly woke up, realized I'd walked a block and do not remember doing it, it can happen while I'm on the phone, anywhere.
My husband will say I'll suddenly stop talking, I have no recollection of going in to it or any memory of where my mind has been, it's always on the other end of it.
Had to go to the ER after having what they thought were 2 large seizures.
My short term memory is completely shot.
I'd definitely talk to a Dr about what happened, good luck.