Which in real life would GET WORSE not better in a matter of minutes.
real life is very different than games.
in real life, if you get stabbed to chest by a dagger or a blade, you take a wound. the wound starts bleeding, you will bleed to death (start to lose hp continously) until you close that wound somehow (bandages, stitches, similar medical treatments). this wound will be closed after a specific time (a very shallow wound will be closed in a day, but a deep wound need weeks). when you get stabbed or shot, the damage can also make you feint and fall down. even after the wound closed, there can be temporal or permanent damage to your organs. even worse, you can lose your organs (permanent Stat damage, and side effects to your character) because of this wound.
if you get punched by someone or mauled with a mace, you will not get a wound (non-hp damage) but your bones can be broken (again, Stat damage and appropriate side effects). simple bruises and muscle damage can be very painful (stamina/endurance loss) and recovery can be a long time. bone damages are also very painful, and you might be wrapped with plaster for weeks, months and even years. if your bones break, you also need to think about nerve, tendon and muscle damages (Stat damage, and restricted movement).
real life anatomical situations can be really hard to simulate for games.
you must to dumb down those things, one way or another.
white wolf settings creates a health system for their games. bruised, hurt (-1), injured (-1), wounded (-2), mauled (-2), crippled (-5), incapacitated. you will get penalties according to what kind of damage you get.
d&d settings have more dumbed down health system. you will get multiplication of hp each level (10 times more hp (blood) at lvl 10). you will get stabbed, zapped, burned, mauled, but you will have no penalty even if your hp decreases to 1. you will fight perfectly with this 1 hp. if you lose that hp too, you will suddenly fall down.
d&d has another weirdness, after you get wounded over and over, if you rest 6 hours, you will miraculously fully recover into perfect condition. however during day time, even if you are just relaxing in your home, you will get no hp regeneration in those 18 hours.
each tabletop p&p game have their different health systems.
but most mmorpgs keep d&d formula because it is more widestream and famous. and of course, it is also easy to implement into the game.