How does that fatigue thing work anyways, I haven't played on hardcoe yet so I have no idea. How much fatigue does it drain? Is it dependent on your unarmed skill? How long do they stay knocked out? Do they keep losing fatigue if you punch them while they are unconscious?
Fatigue works on contact. Once you have "drained" the fatigue of an enemy with enough punches, he/she/it "passes out" for a certain period of time. As for how much, it depends on the type of enemy and, I'm assuming, based on your level. After all, it wouldn't make sense for a level 30 Deathclaw to be dropped in 5 punches right? I can't be sure whether or not its dependent on your Unarmed skill, as damage and fatigue damage may very well be two different things. They stay knocked out for as long as they don't have enough fatigue to stand up. I can't give you much more detail beyond that but I would say at least for 7 - 8 seconds if you don't hit them with more Fatigue damage after they've been dropped. And yes to the last question.
So basically, if you've played Morrowind, the Boxing Gloves, Tape, Cattle Prod *Melee*, and other Fatigue Damage weapons work like that.
Edit: I could be completed wrong with everything I've just said so don't take my word as truth.