I've always wondered if melee 'mech drivers get up there in terms of that emotional/mental "scream as I hatchet or lance or mace things."
The Combine samurai are probably relying more on controlled aggression, where they can turn it on and off due to mental discipline. Fight's on "Banzai!" Fight hard fight hard fight hard...Fight's over. Stop, breath, think, bow.
But I can easily imagine other mechwarriors in a melee machine just getting into that "roar slice and dice" parts flying everywhere, sparks flying everywhere, scream!!!!!"
To the point where that mechwarrior's comrades are having to be wary about accidentally becoming the next target that mechwarrior is going to take a swing at. While you are yelling "friendly!" at them.
And then when you become that hammer...everything starts to look like a nail. So, it could impact your mental state outside of combat as well. I dare argue that's the kind of person you DON'T want driving a melee 'mech. You want a more controlled individual, a disciplined mind, behind that big weapon. But you might not start to see how unhinged they are becoming until it's already happened.