Now I know that "medieval times" is pretty vague, but I'm curious as to how it was dealt with back then. Considering the horrific results on the human psyche during the World Wars and how treating any mental illness for that matter in a humane way is a rather recent procedure, I can't imagine how it must have been hundreds of years ago.
While there is always more that can be written this is a topic (PTSD in pre-modern societies) that has been covered pretty extensively in this sub before and while you wait for a new answer I’ll give you some links. Here is a great post by /u/hillsonghoods on looking at PTSD in history. And here is a link to the FAQ for further reading on PTSD in military history.
This is a common question and basically a comprehensive answer is difficult to find. There are a few answers on this sub which related to ancient evidence/existence of PTSD, about Greece by u/Iphikrates in these posts 1 and 2 (which have links to the FAQ section about PTSD), about Rome by u/sapere_avde in this post 3, and there's a great multi-post on the subject (and the difficulty of its definition) 4.
Basically, the answer is that it is impossible to define and almost impossible to spot in ancient literature; although there are a few cases which seam plausible. While those answers are about the ancient world, we find similar records for United States civil war veterans as well.
Take the case of Confederate veteran William James, who first showed signs of derangement shortly after war's end. Held captive in a northern POW camp, he had emerged physically ill, his mind "much disordered." An Alabama farmer, he tried to restart his old life by putting in a crop in the fall of 1865. But within a year James had become uncontrollably violent. He threatened to kill his father and endangered his own life by jumping in a well in a failed attempt to kill himself...
Civil War soldiers also suffered from delusional paranoia, the kind associated with extreme cases of PTSD. Veteran John Williams was admitted to the Georgia asylum with what we would recognize as post-combat hyper-vigilance - he was "constantly frightened." He constantly complained people were trying to kill him. In a state of extreme agitation, he cut his own throat. Forty-year-old Joseph Pearman, a harness maker from Petersburg, Virginia likewise took his own life in 1875 after protesting that "someone was coming out from the city to kill him."
Cases such as John Hildt 6 show exactly how studying this issue is so difficult. He died in a mental institution in 1911 having been put there some 50 years before after the war ended due to "acute mania." An accurate record of the toll PTSD had on Civil War veterans requires finding such people, reading a modern diagnosis into their 19th century papers, and tracking their life. How many people took their lives due to PTSD in the decades after each of these wars who will never be counted?
Trauma certainly existed in the past, and while it often is completely ignored it is not entirely left out of the historical record. One example comes to mind which honestly I have not forgotten since first hearing about it. This example is a text which ironically was never intended to speak to anyone's trauma at all, it was intended to catalogue unusual happenings which may or may not be of consequence regarding product shortfalls. This example was made by a scribe working under the Persian administration of what is now southern Iraq, and relates a story about female slaves who worked in the temple grinding flour. This was, unsurprisingly, a terrible life for these people; and the brief bureaucratic statement shows this quite clearly in an account which I find quite chilling.
On the 22nd of the month of Ayyaru of the first year of Cambyses, king of Babylon, king of all the lands, Mi:sha:tu, a female serf of Ishtar of Uruk, took a lump of clay in our [administrators] presence and beat a dog with it. We asked her, 'Why are you beating the dog?', and she replied 'I would like to die together with it (ittishu lumu:t).' The dog she beat died of the beating. (End of report)
(YOS 7, 107) 7
I think it would be hard to argue that this person was not having a psychotic break due to trauma. But these references in the ancient world are far and few between.
But let's be specific here and talk about the medieval period. Thomas Heebøll-Holm has looked at the issue, but this esoteric interpretation of what is "between the lines" in texts is not always accepted by other researchers. There are a few literary passages we could point to for evidence, a chronicler of the third crusade recalled knights returned who had "survived unharmed...their hearts were pierced by swords of sorrows from different sorts of suffering." And in the writings of Geoffroy de Charny who wrote books for knights in the 14th century. His instructions for knights include preparations for one's mental health (to put it in modern terms) "When they would be secure from danger, they will be beset by great terrors." 8 And a longer description, with my emphasis added:
In this profession one has to endure heat, hunger, and hard work, to sleep little and often to keep watch. And to be exhausted and to sleep uncomfortably on the ground only to be abruptly awakened. And you will be powerless to change the situation. You will often be afraid when you see your enemies coming towards you...Bolts and arrows come at you and you do not know how best to protect yourself. You see people killing each other, fleeing, dying, and being taken prisoner, and you see the bodies of your dead friends lying before you...
Although this is an interesting interpretation to ponder, we should be careful about subverting the medieval author's intent. A great example of this pitfall is given here 10 where u/michaeljonesbird (as had u/Lard_Baron before) cited Shakespeare's Henry IV (1590's) as evidence of historical PTSD, going quite in depth in the similarity of symptoms. In the scene, Lady Percy, the wife of Hotspur, is asking him about his recent disturbed emotional state:
Why do you bend your eyes to the earth, And start so often when you sit alone? Why have you lost the fresh blood in your cheeks; And given my treasures and my rights, To you to thick-eyed musing and cursed melancholy? In your faint slumbers I by you have watched, And heard you murmur tales of iron wars; Speak terms of manage to your bounding steed; Cry 'Courage! To the field!' And you have talked, Of sallies and retires, of trenches, tents, Of palisades, frontiers, parapets, Of basilisks, of cannon, culverin, Of prisoners' ransom and of soldiers slain, And all the currents of a heady fight. Your spirit within you has been so at war, And thus has so stirred you in your sleep, That beads of sweat have stood upon your brow, Like bubbles in a late-disturbed stream; And in your face strange motions have appeared, Such as we see when men restrain their breath, On some great sudden hest. Oh, what portents are these? Some heavy business has my lord in hand, And I must know it, else he loves me not.
This seems like pretty convincing evidence! But in fact, this is neglecting the time-line, as u/butter_milk pointed out [10]: these night terrors are happening because Hotspur is racked with guilt over his conspiracy. These are terrors of future battles which are already weighing on his honorable conscience. But, this hypothetical situation remains. Shakespeare here has created a plot point in which his characters play out their lives, yet a plot point which could be realistic - night terrors about war experiences...? This isn't my period so I'd be happy to hear a more detailed understanding of these sources or the practicality of events in Shakespeare. But continuing on, I can give more evidence about more clear-cut examples of medieval PTSD if we turn away from Europe.