Before "modern" warfare/weaponry (I'll say pre-American Civil War for the sake of this question) it seems that, while the death and casualties weren't as astronomically high, the fighting itself seemed more personal. There's data on the psychological stress and trauma that comes with war today but I can't even imagine the level of desensitization a soldier would require if killing an enemy required looking at them while you impaled them with a spear or sword.
I know even the concept of psychology is relatively new but I'm curious as to whether we have any accounts on the effects that more personal brand of warfare had on soldiers. What do we know in general?
Please search the subreddit for similar questions, I've seen this answered multiple times, dating from Napoleon to Ancient Greeks.
For the sake of answering your question though, yes. PTSD was among soldiers before modern warfare. For example, there is an ancient Greek veteran named Epizelus, as told by the early historian Herodotus, Epizelus was a gigantic man, with a large beard yet lost his vision shortly before engaging an army of Persians. After the battle, army physicians examined him and could not find a single wound on him, only Epizelus would tell them that he lost his vision before the Persians attacked. He never regained his vision.
There are many more examples, I've seen accounts of knights regarding the terrors of battle and how the loss of life was haunting, Napoleonic soldiers breaking down into fits of terror etc.