You fall to the ground! said my Dwarf Fortress HUD before i knew that i should never travel by night, motherfucking Boogieman.
BUt ok, what about to add that function to Cataclysm? That you can crouch and/or fall to the ground, and you make a just a bit of noise and you are usually unnoticeable. Like DayZ. But EXTREMELY slow. Also getting up would take 200 action points.
And with some good hits, like having an awesome punch from a Hulk, to fall to the ground and got a bit knocked. This would add realism and “difficultiness” to the game.