I've been there. In my teenage years, when my PTSD was much more raw, and I had a drinking problem to boot, I'd fly off the handle a lot. People invading my space was the number one reason. I used to have a female friend who liked to come up behind me in the halls of the high school and 'surprise hug' me. Nothing sexual about it, but the unexpected physical contact caused me to jump and scream EVERY TIME. Eventually she learned, and got my attention first.

When I'm more prepared, I can handle it much more rationally. I'm still that way. If it's sudden, I freak. If it's expected, even like a tiny nagging suspicion in my mind, I have more time to decide how to react.