As I mentioned in an earlier post, What Price Glory and Hit Points, Dave has an interesting change to hit points in his What Price Glory rules that splits hit points into two parts. I did something similar back in the late 1970s. Here's a brief explanation of how the Body Point/Fatigue Point system we used worked. It's very similar in concept to Dave's rules but somewhat different in the details.
A character's or monster's Fatigue points are equal to their hit points under whatever normal rules you use for determining hit points.
A character's Body Points are equal to his Constitution (plus 1 per level for fighters up to a maximum of +10).
Most monsters have zero Body Points and are considered dead when they run out of Fatigue Points. Important ("boss") monsters can be given Body Points at the DM's option, their Body Points are equal to the number of hit dice the monster has multipled by the monster's "size factor": 1 for smaller than human, 2 for about human sized, 3 for large (horse-sized), 4 for very large (giant or dragon-sized).
Damage is applied to Fatigue Points until fatigue points reach zero when excess damage (and future damage) is applied to Body Points. When Body Points reach zero, the character is dead. Body Point damage recovers at the rate of 1 point (plus Constitution bonus) per full day of rest. Magical healing restores 1 Body Point per level of the spell or the normal dice of healing to Fatigue Points.
Provided the being is at full Body Points, Fatigue Points recover at the rate of 2 (plus Constitution bonus) points per full 10 minute turn of rest and will recover completely with a full night's sleep. If a character has taken Body Point damage, Fatigue Points recover at the rate of 1 (plus Constitution bonus) points per full hour (6 turns) of rest and will recover to their Wound Limit with a full eight hours of sleep. Wound Limit depends on what percentage of Body Points the character has remaining:
76 to 99% BP Remaining -- Wound Limit is 75% of maximum FP
51 to 75% BP Remaining -- Wound Limit is 50% of maximum FP
26 to 50% BP Remaining -- Wound Limit is 25% of maximun FP
1 to 25% BP Remaining --- Wound Limit is 10% of maximum FP
This system makes it more obvious that hit points aren't really hard damage, just the character's ability to not take meaningful damage. Provided the character does not take real damage to his body, fatigue points recover quickly. Real damage, however, takes longer to heal and reduces the character's energy level if he chooses to press on with activities instead of taking to his bed and resting to heal.
Some obvious additions can be made to this basic system if one wishes to do so. For example, critical hits might do damage directly to a character's Body Points equal to the number of hit dice rolled for weapon damage. If your house rules use spell points, you could simply reduce Fatigue Points instead. Etc.