Thank you for writing about this difficult situation. I appreciate the opportunity to comment on it.
I would begin by keeping a log. Include what you were talking about and exactly what thoughts were interrupted. When you “return” notice what it is that allows you to refocus. A log of what you were doing or thinking about before the session, and what you were planning to do afterward opens the window a bit wider to look for possible activators. The log helps reveal patterns that may not have been indicated in a session.
For lack of a better definition a dissociation is a psychic numbing. Almost always this happens for the purpose of protecting you. It seems to serve a dual purpose in that it protects, but also leaves clues where the protection is needed. This may take a while, and I have been amazed by what was eventually revealed by the people with whom I’ve worked. Yes, it is often trauma, but on occasion there have been other things I hadn’t expected.
One word of caution: Whatever this is protects you, and we don’t know from what, so don’t push too fast. We don’t want to remove something that is trying to help without understanding why it was put there in the first place. Stay interested in the process and allow your new relationship with your therapist to grow. The joint exploration and journey to unravel this mystery is often as valuable, if not more so than what is revealed.
Wishing you patience and peace,