1) Hand-to-hand combat where your fate is decided within a few seconds but you have some control over the situation.
2) Sitting in cover while artillery shells rain down randomly around you.
Being in constant danger for days (like WW1 trench warfare) is more traumatizing for a human.
http;//www.acoup.blog had some excellent posts about this recently.
For a relatable example, compare driving a car to riding in a rollercoaster. Driving is more dangerous and you're not really in control of other drivers who can hit you, but you feel in control because you hold the wheel.
Not to mention that modern war is way, way, way more deadly.
Even unarmed fights are usually shorter than portrayed in popular fiction. If ancient battles lasted days, that's because they were organized to move combatants around and avoid actual combat until advantage could be taken. Melee between two groups of armed humans could be over in less than a minute. Note that the most common way for melee to cease would be for the losing side to retreat (perhaps without those of their number who had already succumbed), which is viable when ranged weapons aren't used.