I propose to split a creature's hit point (hp) total into two parts: body points (bp) and resilience points (rp). The rules for using bp and rp are largely in the Injury and Death section; the rules for determining your healthy bp are in the Human body section, and for determining your rested rp are in the Fighter class.
This is an old solution to an old problem - the realism questions raised by high-level characters having hundreds of hit points, rivalling giants and dragons. How can a flesh-and-blood human withstand a dozen strong sword blows, or a fall from a mile-high cliff?
Within the official rules the GM can try to make the action sound realistic by describing most of the hit point losses as not involving real injury, and only describing serious bodily damage as the last few hit points are reached (personally, I prefer to get clear prompts for this sort of description from the rules, rather than have to judge it myself while thinking about all the other aspects of running combat).
There are also rules such as death from massive damage and coup de grace that seek to prevent the most implausible consequences of the basic system. However, I still feel that high-level characters have too much chance to survive massive assaults largely unscathed. It is particularly glaring when the hazard is something non-fantastical like a fall or an avalanche of stone.
One old solution to this issue is to divide hit points into a realistic and fairly permanent number that reflects the body's ability to withstand real injury, and a more open-ended number that reflects the ability to avoid it, and its increase with experience. This then opens up the possibility of certain hazards getting directly to the real-damage points.
With my separation of body levels and experience levels, there's a very obvious way to implement this idea - body levels grant body points (real damage resistance), while experience levels grant resilience points (a finite ability to keep avoiding real damage).
Certain types of hazard are more deadly to many high-level PCs and similar NPCs. These include attacks and effects with high damage from a single source, attacks and effects that are not subject to armour, and situations that don't allow you to use your combat skill. It is easier than in the official rules to die or be taken down despite having plenty of hit points (rp) left.
Conversely, it is easier to survive personal defeat in combat. If you have converted a lot of the damage in a fight into rp, you may go down with negative rp and still most of your bp. In this case you have a good chance of recovering a short time later with few or no ill effects (depending on which side wins the fight and what they decide to do with the wounded...).