Dissociation is often part of PTSD. If you have PTSD, I would be surpised if you didn't dissociate. People with BPD dissociate a lot too btw. It's hard to distinguish between just being lost in thought, and dissociating. I know that I dissociate a lot, but it's hard for me to notice it. A lot of the time I think I'm just distracted and thinking about something, but that's what dissociating is if you are so distracted and lost in thought that you lose connection with here and now while you are gone.