I've heard anxiety is sorta like your sense of danger... Like adrenaline building up, but it's not expended, leading to the various situations of anxiety. And it would fit with just about every situation too, especially PTSD. That being said, as far as I know and the first couple pages of google :p, we don't really have any medicines, and few drugs that actually alter the brain structure itself, and those are largely via destruction, or... I'm not a scientist so I'm not sure how to word it, but, however stuff like heroin and cocaine produce the situation necessary to cause withdrawals.
So for the most part, at least currently, and w/o professional knowledge(though in this field... lol), medications can fiddle with the interactions, such as anti-psychotics, ssri's, blah blah blah, or ease the anxiety, but they can't solve the issue alone.
Now into just an opinion, if we are able to form connections that don't fade with the particular thought, such as habits, and learning things by "muscle" memory, it doesn't seem like much of a stretch for things like PTSD to be a flash version of that, especially given the circumstances lol, and the fact that many people who develop it or maybe including other anxiety disorders, have a definite lack of the "lock and key"(stolen and probably used incorrectly from "Dollhouse"), feeling of safety afterward. Like a kid who falls off a trampoline and his parents laugh at him, telling him not to be a wuss. Chances are, if the kid is young enough and doesn't know much about the trampoline, the fear is probably gonna linger. If it never gets addressed(or he never gets back on the trampoline lol) it would make sense if it developed into something more intense. 'Tis a minor example, but I'm not gonna list the more gruesome examples.