[Boromir88]

There is always one part in the book when I look and I can't help but say this is Tolkien remembering his war experience...or putting it in the story. And that is when Sam sees the dead Haradrim and starts to really think about him as a person:

It was Sam's first view of a battle of Men against Men, and he did not like it much. He was glad that he could not see the dead face. He wondered what the man's name was and where he came from; and if he was really evil of heart, or what lies or threats had led him on the long march from his home; and if he would not really rather have stayed there in peace - all in a flash of thought which was quickly driven from his mind.~Of Herbs and Stewed Rabbit

I look at this and you really do get a sense that this is some sort of memory of war Tolkien had put in the story.

At first look I would be quick to down and squelch your surmise ...because of this:

Its real war does not resemble the legendary war in its process or its conclusion.~Foreward to LOTR

But if we look at this, it seems like Tolkien is saying that the main storyline doesn't resemble World War I (or II for that matter). Well if we look at that scene with Sam, that moment is not dealing with the main storyline. It's a step away from the story. It's Sam stepping back from the events of the story and reflecting. Basically the part where Sam sees the dead Haradrim has no importance on the storyline, or the War of the Ring at all. It is Sam stepping away and reflecting.

So, to get more onto the topic of PTSD, I think it's quite possible that we can see signs of PTSD with Frodo or Sam (or other characters):

An author cannot of course remain wholly unaffected by his experience, but the ways in which a story-germ uses the soil of experience are extremely complex, and attempts to define the process are at best guesses from evidence that is inadquate and ambiguous. It is also false, though naturally attractive, when the lives of the author and critic have overlapped, to suppose that the movements of thought or the events of times common to both were necessarily the most powerful influences. One has indeed personally to come under the shadow of war to feel its oppression; but as the years go by it seems now often forgotten that to be caught in youth by 1914 was no less hideous an expreience than to be involved in 1939 and the following years. By 1918 all by one of my close friends were dead.~ibid

Tolkien goes on to reject the idea that the Scouring of the Shire was a reflection upon England after WW1, except some loose similarities at best. Anyway, if it is something that deals with the main plot/storyline, it would be hard to try to create an argument that there was any bearing on the World Wars. The Scouring of the Shire was an important and essential part to the story. However, when trying to find PTSD with the characters in the story, I think it would be entirely possible...as it wouldn't play into the big plotline of the story. Just as Sam reflecting and thinking about the dead Haradrim soldier did not play a part in the plotline of the story. It was Sam stepping away from the action for a brief moment and thinking about him as a person. So, naturally when I read that part, I automatically think 'this may be Tolkien's war experiences and memory coming into the story.'