Eve I don't have PTSD but my whole life I would run whenever I got upset or just felt I had to get away. When younger from 10 - 15 it was to a place I had in the woods that was "mine" a place that felt safe and "away" from everything. In my teens I would run to friends houses sometimes for days or weeks. I didn't graduate high school because of a time I ran with a friend to Massachusetts. I came back later and went back to high school for the last half of the year. Then I got pregnant and ended up running again with friend after a traumatic time period to Fl. and again didn't graduate high school. I didn't come home until I was almost 6 months pregnant and only then because I had to realize what I was doing was going to affect my child and not just myself from then on.
Have you ever thought to work with this feeling by making some sort of safe place to be able to run to? rather then trying so hard to fight it? I know it can be almost painful to fight it sometimes with an almost claustrophobic feeling if you make yourself stay. Anyways just a thought as to how you can work on dealing with it.