Hit points are generally a compromise between fast and easy gameplay and realism. A problem is naturally that real battle never work like hit points, so I’m taking a pragmatic view on the topic.
What Hit Points Are
Hit points are a combination of minor injuries, exhaustion, emotional shock and simple “battle luck” in a combat. Losing 90% of your hit points is not the same as having a sword stabbed through your lung, it’s simply a game mechanic to show your luck is about to run out, and you know it. Whatever the case, at -10 hit points, you ARE dead.
This also explains how hit points can regenerate so quickly; the loss of hit points only marginally represent actual injuries. In most cases they represent bruises and weariness rather than injuries.
As an attempt to bring some realism and keeping as much as possible of the relatively quick gameplay of DnD, I added Wounds. These are actual injuries on a player and these takes a lot longer time to heal than “just a loss of hit points”, while at the same time mostly have a pretty small impact on gameplay. In worst case scenarios, however, they DO affect gameplay, and to keep having to fight day after day will bring a character to a point where they will be easily defeated or even die.
This mechanic adds the requirement of the players to find a way to heal up before the next encounter, be that through expensive magical services or through spending days or weeks in bed taking it slow.
Because most wounds simply accumulate, and are “manageable”, a character can have several at once without a massive issue. However, if she is unlucky and receives another wound which gives penalties, it will take a very long time for the body to heal that wound, since it’s also healing all the other wounds at the same time.
Wounds then don’t become a massive nerf or killability of characters, but a somewhat realistic system to make them slow down their pace, or at least be very careful, if they have a couple of wounds.
Death itself can be through shock, cardiac arrest, massive organ failure, asphyxiation or simply bleeding to death. The dying status represents one or all of these effects, while the shock status added by me specifically deals with shock only.
In this particular campaign setting, ressurection is very uncommon, so as to alleviate this, I’ve added a new spell, Resuscitation, which will work in very limited circumstances, more similar to a skilled paramedic of today than an actual Raise Dead spell.