I saw your title and was going to respond to something along the lines of World War II, since that is my expertise, but then read the 1700-1800s bit. I know that during the American Civil War cowardice in battle was known as "Yellow Heart" or "Soldiers Heart". There are many documents of Civil War veterans turning to booze, and in the big cities turning to booze and opium, and other drugs. We need to remember that this was a time when counseling and therapy just did not exist, and was looked down upon. If you needed advice or some sort of counselling you got it from your Priest or Pastor, or from friends, or a trusted family doctor. There certainly was not any form of anti-depressant, anxiety, or other medications that are prescribed now-in-days to soldiers (and others) with PTSD.

Now on to World War II, PTSD was known as "Combat Fatigue" and in many cases was a legitimate reason for a soldier to be pulled off the line, and considered wounded / injured. The book "The Deserters: A Hidden History of World War II" by Charles Glass is a biopic anthology that follows a few soldiers who deserted in World War II (with Europe and North Africa being the main focus). Almost all of the deserters deserted because of Combat Fatigue, and because they just refused to return back to front line service. Many of these guys had lost friends during the war, and had seen action for many continuous days and just could not take it any more. One example is a Scotch soldier fighting in North Africa who witnesses his entire unit get decimated. He tried fleeing, was captured, imprisoned and then sent to another unit. Then there was an American solider who experienced a lot of combat throughout France and could not take it anymore, and basically fled to Paris, and was heavily involved in the black market - including robbing military and civilian stores. A lot of that had to do with PTSD reasons. They just could not handle being at the front, and refused to go back, so did anything they could to survive.

However, most soldiers who suffered from PTSD were honorable, brave, and suffered in silent. It was not until after the war that the PTSD really started showing itself. For example, many soldiers turned to drinking - including the famous Louis Zamperini the famous World War II pilot whom the movie and book "Unbroken" is about. He suffered severe alcoholism after the war, which led to a failed marriage - all because of what he suffered, and his reliving of his sufferings at the hands of the Japanese. The book "Unbroken" goes in to Zamparini's PTSD after the war in great detail. Another example is Buck Compton, in the miniseries and book "Band of Brothers", he was a Platoon Commander in the 101st, who eventually was pulled from the front lines because of Combat Fatigue. He later had a great life. But he still had his demons.

Almost EVERY World War II autobiography / biography / journal from ANY side of the war, shows that the author returned home with some sort of PTSD. Drinking, night terrors, being reserved from society etc... almost all of the veterans had it to some degree or another, but don't call it PTSD or Combat Fatigue. They just talk about drinking, or doing whatever to try and forget.

The 1946 fictional (but historically accurate) movie "The Best Years of Our Lives" delves heavily in to how PTSs (without calling it that) profoundly impacted returning servicemen in many different way.

Sorry I could not help that much on the 1700-1800 aspect, but I can point you to many sources in regards to World War II.