The thing to remember is that being a runner is moments of 'high excitement' with a lot of 'boring' stuff going on around it, and that's just when you're working, to say nothing of your 'off the clock' life. It isn't like you're in the arena constantly fighting again and again and again, or stuck in a zombie apocalypse having to fight your way out of the sprawl.
Now, those moments of high excitement, especially the fighting, can have psychological impacts. Losing buddies in crossfire can be bad. But metahumans aren't exactly fragile (mostly) and you can find a lot of ways to cope with some real serious drek. If you wanted to make a real study of it, you ought to look at the ways cops and gang members cope with things in RL.