Having worked with these for my "bodyarmor" script, these are my findings:
1) Unlike OFP, it's impossible to revert the deadstate of a living unit: once they're dead, they're dead.
2) Native "dammaged" and "hit" eventhandlers are both slightly too slow when used in the traditional "unit setdamage 0" (or "unit setdamage 0.8") way : quite often the unit will be killed by two consecutive shots, or a single lethal one from close range. And, as mentioned, once they're dead they're dead. SOMETIMES it's possible to get a "living" guy who's lying dead on the ground and who'll tell you to hold fire when you shoot at him, but he'll be immobile forever (no way to get out of a "deadstate" playmove either)
3) To fix this it is possible using either the "dammaged" or the "hit" eventhandlers to give the unit negative health: unit addeventhandler ["hit", {_this select 0 setdamage -5}]; However using the "dammaged" eventhandler here is very much not suggested: the "dammaged" eventhandler FIRST calculates damage and where the hit took place, and then runs its attached script: this means the unit might very well have been killed before it was healed again. The hit eventhandler registers a hit and runs the script. And no: if you have a "hit" eventhandler that resets health to -5 all the time, and a "dammaged" eventhandler to boot, the "dammaged" will never run since the damage never has time to register before the "hit" resets it.
So in short: it is impossible (AFAIK) to leave a unit at 0.8 health until someone shoots them in the head - I'm guessing this is for some kind of zombie script, correct? Or, correction: if the unit would have an armor value bordering that of a tank, it would be possible, except for the fact the "dammaged" (or "hit") eventhandlers are rarely run when the damage is that tiny.....
In other words, it's not really doable without an addon. Hence: go look for zombie-addons for all your zombie-bashing needs! There're a couple
(I might be wrong of course!)
Wolfrug out.