You may find these threads address some of your question.

http://www.reddit.com/r/AskHistorians/search?q=PTSD&restrict_sr=on&sort=relevance&t=all

I know one of our commenters (/u/donaldfdraper?) has written about the evidence for Marechal Ney suffering from PTSD.

The general gist, however, is that there was no systemic practice of psychology in the 18th century, and a number of cultural conventions limits the amount of documents generated about the emotions of common soldiers.