Hit points represent a character’s ability to withstand damage and keep fighting. A character’s base hit points are equal to twice their Constitution score, plus any points gained from their race or class. A character gains a certain number of maximum hit points based on their level; these are added to their base hit points to determine their total maximum hit points.
Attacks which would harm your character are normally subtracted from your hit points. A character who has lost half their total hit points is bloodied; certain actions and effects only affect a bloodied character.
If you would take more damage than your current hit points, your hit points drop to zero - you never have "negative" hit points. However, if you would take more damage than your hit points plus your heal value, reduce the amount of damage that you would take by your heal value, and lose one point of Vitality. Continue converting hit point damage into Vitality damage until the total damage does not exceed your hit points + your heal value.
While hit points represents a character’s ability to withstand damage, vitality is a measure of a character’s actual health and survivability. Your character has a Vitality score equal to 5 + his Constitution modifier.
Whenever you are reduced to 0 hit points by an attack, you are dying, and must begin making Endurance saving throws during each of you turns to attempt to stabilize; each failed saving throw causes you to lose a point of vitality. This means that characters who come back from the dying condition will have slightly less reserves available to them until they spend a day or more resting and recuperating.
Critical hits, the dying condition, and certain particularly grievous attacks can cause damage to your vitality. Whenever your character (or any creature) suffers a critical hit, it automatically suffers one point of vitality damage. If the critical hit deals more damage than the creature's heal value, it loses an additional point of vitality due to the severity of the wound. If the critical hit deals more damage than its bloodied value, it loses yet a third point of vitality.
When your character's Vitality is reduced to 0, any further damage that would reduce their vitality instead deals additional damage equal to their heal value. If a character is out of vitality and hit points, they are dead.
Each point of vitality provides you with one Healing Reserve, which is an expendable resource that represents your ability to push through pain and reinvigorate yourself to keep fighting. Various actions allow you to spend a healing reserve; when you do, you regain hit points equal to your heal value, which is equal to half your bloodied value, rounded up. When you take Vitality damage, you also automatically lose any reserves in excess of your new Vitality, which you cannot recover until the Vitality damage heals. If you have already spent more reserves than your current vitality, you do not lose a reserve when you lose vitality - the reserve that you would lose was already spent.
Whenever you take a short rest, you may choose to spend any number of healing reserves, regaining hit points equal to your heal value for each reserve that you spend. If you have per-encounter feats that allow you to regain additional hit points when you spend a reserve, you may use each of those feats once during the Short Rest.
Whenever you take an extended rest, you regain a number of hit points equal to your heal value times your remaining reserves, then regain 1 point of lost Vitality if you have taken any Vitality damage. You then regain all reserves up to your current Vitality.
Optional Rule - Lingering Wounds
Characters who want to play a more gritty game may utilize the following rule for detailed critical hit damage:
Whenever a character suffers one or more points of Vitality damage due to a critical hit, roll 1D20 + the amount of vitality damage lost to the hit, then subtracts the target’s Fortitude defense. Apply the indicated condition (if any) until all of the target’s vitality damage is fully healed.
Roll Result Lingering Wound Effect 0 or lower No Effect 1 to 2 Cannot use main hand 3 to 4 Cannot use off hand 5 to 7 Slowed 8 to 9 Weakened 10 Deafened 11 Blinded 12 Dazed 13 or higher Stunned
Particularly gritty settings may wish to force players to make an Endurance roll during each extended rest in order to regain a point of vitality; a failure means no vitality is regained during that rest, while a critical success means two points are regained, and a critical failure means that one Lingering Wound effect becomes a permanent affliction until healed with high-level magic. One character may make a Heal check once per day to attempt to aid healing; if they succeed, one additional point of vitality is healed, and on a critical success two additional points are regained. A critical failure on this Heal roll should be treated as a critical hit from a weapon, inflicting damage equal to the character’s reserve value.