I was thinking about this and found this thread, so I thought I would chime in.
Our brains are computers. They have various operating systems and programs that enable it to function in a wide variety of situations. One example of a computer program would be the fight or flight program. This program is specifically there for our brain to respond to danger.
However, something comes along, and your computer program develops a programing glitch. It causes change in the program, and allows all kinds of pop ups on your computer. So now when certain keystrokes are entered into the computer instead of the expected result, you get an entirely different response, you get all these horrible pop ups, so you cannot use the computer in the way you need, or want.
So PTSD is a malicious pop up that shows up when certain keystrokes, triggers, are entered, and instead of a reasoned response to the keystroke, we have an unreasonable response, but the reality is, our response is not to the trigger, but to the original situation that caused the glitch in our computer programing.