Healing

Once a character is wounded, his player will naturally want to get him healed. Characters can heal either by natural or magical means. Natural healing is slow, but it's available to all characters, regardless of class. Magical healing may or may not be available, depending on the presence (or absence) of spellcasters or magical devices.
The only limit to the amount of damage a character can recover through healing is the total hit points the character has. A character cannot exceed this limit until he gains a new level, whereupon another Hit Die (or a set number of points) is added to his total. Healing can never restore more hit points to a character than his maximum hit point total.

Natural Healing

Character's heal naturally at a rate of 1 hit point per day of rest. Rest is defined as low activity — nothing more strenuous than riding a horse or traveling from one place to another. Fighting, running in fear, lifting a heavy boulder, or any other physical activity, prevents resting since it strains old wounds and may even reopen them.
If a character has complete bed rest (doing nothing for an entire day), he can regain 3 hit points for the day. For each complete week of bed rest, the character can add any Constitution hit point bonus he might have to the base of 21 points (3 points per day) he regained during that week.
In both cases above, the character is assumed to be getting adequate food, water, and sleep. If these are lacking, the character does not regain any hit points that day.

Magical Healing

Healing spells, potions, and magical devices can speed the process of healing considerably. The specifics of such magical healing methods are described in the spell descriptions in this book and in the DMG (for magical items). By using these methods, wounds close instantly and vigor is restored. The effects are immediate.
Magical healing is particularly useful in the midst of combat or in preparation for a grievous encounter. Remember, however, that the characters' opponents are just as likely to have access to magical healing as the player characters — an evil high priest is likely to carry healing spells to bestow on his own followers and guards. Healing is not, of itself, a good or evil act.
Remember that under no circumstances can a character be healed to a point greater than his original hit point total. For example. say a character has 30 hit points, but suffers 2 points of damage in a fight. A while later, he takes an additional point of damage, bringing his current hit point total to 27. A spellcaster couldn't restore more than 3 points to him, regardless of the healing method used. Any excess points are lost.

Herbalism & Healing Proficiencies

Characters can also gain minor healing benefits from those proficient in the arts of herbalism and healing. These talents are explained in Non-weapon Proficiencies.