So a slow death and a quick one
The quick one resulting from head shot, should have a shocking feel to it, like an instant black screen with and becoming deaf right after the sound of the hit.
Slow one should have fading and/or filter added to the surrounding sounds and the screen would get more and more blurry(blurry already there) turning black at the end.
Maybe loud noise when suffering death from explosion(like Arma 2)
The sound immersion really needs a boost when playing vanilla Arma 3