A lot of investigative horror adventures unfold over the course of a few days or weeks. Taking characters out for a realistic six-month hospital stay basically means the player has to make a new character or sit out for the rest of the game, neither of which are fun.
And it's not like being at full HP will help that much against really scary things.
Hi Lyme - fair enough. Lurking Fear bills itself as simulationist horror, so an instant return to full health after being shot a couple of times (or what have you) had me raising my eyebrows. I think I will house rule that hit points return at 1 hit point per night of rest. Or perhaps a return to full hit points per the rules as written, but all physical acts are at -30% the next couple of days to account for lingering effects. Cheers!
It's a bit of a weakness of hitpoint systems. A common response is to view HP as representing fatigue and minor injuries that gradually weaken a character until, at zero hp, they finally take a truly dangerous injury. In practice, I've never seen a player or GM resist the temptation to describe attacks that reduce HP as causing serious trauma to the flesh. Still, HP is a feature of most older d100 horror games, so it needs to be a feature for maximum ease of compatibility.
I am working on a more modern horror system that will not use HP at all.