Depends, because we had millenia of wars, even much more gruesome (but without explosions), and much fewer accounts of psychological shit. It was just a fact of life, and most people carried on.
But the way you've phrased it implies a bit more and you should probably clarify.
It may be the case that being from a society in which violence is glorified and made into a virtue makes people less susceptible to war-induced PTSD. Or the circumstances of the war could make the difference; if you are fighting a just war you earnestly believe to be in the direct defense of your family and community, or whether you were drafted into a war that has nothing to do with you and society tells you is cynically or foolishly motivated.
I think it's a mistake to look at a civilisation past or present that is defined by widespread violence and death and think of it as anything other than dysfunctional. It's just that the baseline of suffering is so high it drowns out all the easily identifiable forms of suffering we're accustomed to.
You often hear people talk about the cultural trauma of Japan, Russia, or Germany. As an outsider there's also a clear circle of violence in American society which pervades and informs cultural attitudes, social policy and conflict resolution. This shouldn't be surprising given the US's history of widespread suffering throughout its history: indentured servitude, religious prosecution, chattel slavery, genocide, disease, civil war. American hyperindividualism as well as both the Cold War and War on Terror "world police" eras of foreign policy and the more recent popularity of isolationism have all the trappings of a trauma response.
Meat is violence. This is why slaughter is often highly ritualized in "primitive" societies, often thanking the animal for its part and being deeply aware of the interplay of life and death that meat eating requires but also the importance of the slaughter for the survival of that society. Both the meat-eating urbanite having an existential crisis over having to kill an animal for sustenance as well as the farm hand thoughtlessly killing an animal are in unhealthy positions - one from the detachment of mass production, the other from the desensitization of their involvement in it. The vegan might be in a healthier space but given modern industrial production is likely as detached from the food they consume and the suffering and death that enables it (be it the field hands working in bad conditions for low pay, the animals dying in the process of industrial farming or the ecological damage caused by shipping exotic or out-of-season produce around the globe).
I say that as a city dwelling meat eater living in Germany, which is a deeply unwell country scared of understanding its own history beyond easy platitudes and simple stories of good and evil people. Humans are not a virus but humanity is very sick and it will take a long time and a lot of effort for it to get any better - if ever.
More to the point: as someone who has had a justified need for therapy before, I think it's important to recognize that of course you can often simply "push through it" because if you can't, you simply break. But importantly you won't get any better, you will just appear more functional for as long as you can keep it up. Therapy was a taboo in my lifetime and I'm not even 40. Suicide is still often a taboo but only started being acknowledged a few short decades ago because a number of celebrity deaths became widely publicized (in Germany it was a soccer player, the stoic masculinity equivalent of an American quarterback). That didn't mean these things didn't happen before. It just meant we didn't acknowledge they did and we didn't know how to get help.
Yes, there are people who aren't "bothered" by killing animals. There are also people who aren't "bothered" by killing people. I'm saying that's a bad thing. I live near an industrial slaughter house, in fact one of the biggest "meat factories" in Europe. The people who work there are not okay.
I'm not saying "don't eat meat". I'm saying if eating meat literally doesn't bother you, you should consider that a warning sign.
You were using the wrong words, that's it. I think it would be good for you to use the right ones instead, for several reasons, one being that you might not get mistaken for a Ruggiu kind of person.
The aristocracy generally fared relatively well in medieval battles as it was more profitable to capture a noble unharmed for ransom than to risk severely injuring or killing them, not to mention the class taboo and difference in training and equipment between a noble and a commoner.
But warfare was also extremely different. The use of crossbows against Christians was banned by the Catholic church because it was considered too horrifying because of its speed. Battles would often be won by forcing the other side to surrender or morale breaking down and being routed. Because the violence was also much more direct than the pull of a trigger or press of a button, humans were also much more hesitant to actually try and kill their opponent. The crusades are infamous because they actually involved a more modern level of dehumanization but throughout most of history wars would be fought against people who looked like you, spoke a similar language and shared a similar culture. The exceptions are so well-known because they were rare.
"It was just a fact of life" is something we say about all kinds of horrors of the past. You say "most people carried on" but this is literally survivor bias: most people who served in past wars don't go on to kill themselves even without treatment even when they suffer from PTSD or shell shock or whatever. That doesn't mean recognizing and treating their condition wouldn't drastically increase their quality of life. It also ignores that "most" is not all. People would simply starve themselves to death or go into the woods and never come back or get "battle frenzy" and throw themselves at the enemy with no regard for their safety and that too was "just a fact of life" but today we would call that suicide.
History is full of "psychological shit". We just lacked the understanding of psychology to properly classify and recognize it in ways that would allow us to address any of it.
Also throughout history there just wasn't much attention for regular people, and they're seriously under-represented in the historical record in pretty much every way. Do you think some Roman general is going to write about his soldiers crying about how horrible war is? Of course not; that would make him and his army look bad. He was much more likely to under-represent his numbers to make his army look good ("we defeated the Barbarian horde of 50,000 with just 5,000 soldiers!" sounds a lot better than "our armies were of equal numbers but we won"). And the soldiers themselves typically didn't leave any records.
And throughout much of history there just wasn't all that much attention for these types of problems in the first place. Patton famously slapped some soldiers dealing with shell shock because he thought it was just fake and they needed to "man up". That was probably more or less the typical response for much of history.
So not surprising to see some brain damage in navy seals. Of course the question is what comes first, the brain damage or the ptsd. And whether something can be done before brain damage happens in terms of medication or therapy.
Psychological doesn't mean "imagined", just means "in the realm of thought". Your thinking is not "imagined", nor is the impact of decisions, ruminating, etc to you.