Might want to check out this thread, as it covers the same material and is pretty recent:

http://www.reddit.com/r/AskHistorians/comments/1zpcry/how_was_ptsd_posttraumatic_stress_disorder/

This is a very popular question and actually has a FAQ entry that's worth checking out.

This might help too

http://io9.com/5898560/from-irritable-heart-to-shellshock-how-post-traumatic-stress-became-a-disease