I've been playing for about a week now (single player campaign), and really wish there was an option to self heal to 100% using the First Aid Kit.
As it stands it seems you can only heal yourself to 75% of full health, meaning that from that point onwards you can't aim properly, you have very little stamina, and you end up grunting (like a pornstar - as others have mentioned).
For me personally, I'd rather have a configurable option to allow self healing to take you to 100%. Maybe make FAKs harder to come by to compensate? But for me, I find it frustrating that if you get hit early in a mission, you know you're faced with playing the remainder of the mission in a nerfed state.