Moment of panic

I've been on busses the day after busses have blown up, I've walked around town and seen debris from bombings left over, I've spent time in neighborhoods being shelled and so it came as a shock to me when I felt a panicked. My class was starting and the teacher asked for the door to be closed. I looked at the closed door, looked at the windows (a story above ground level) and I started being bombarded with thoughts relating to the Virginia Tech shooting - can I jump out?! What would happen if someone came in with a gun! I'm sitting in the inside of a row! As these thoughts and others were attacking my thoughts a funny thing happened. A guy with a gun did walk in. I immidately breathed a sigh of relief and then laughed at myself, about 1/4 of my class packs heat...