So, in RPGs, healing is essential, due to the number of ways that you can get hurt, sliced, crushed, poisoned, slashed, punctured and bitten. Especially if you're going around getting into fights.
In real life, we use natural healing, pharmaceuticals, and surgery as the main ways of fixing injuries, with a bit of medical practise thrown in.
A word here on my RPG system of choice - Dragon Warriors, although not too dissimilar to D&D, has a lot less hit points going around. Rather than increasing your total by a dice roll every level, you get an extra one health point to your total with every rank gained, if you're a fighter type, and if you're a spell caster, one point every second level. So people are more fragile and die easier, even at high levels. There's really no chance to be a 'tank' in these games, and armour is VERY important
The first and most obvious method is recovery after battle. I've seen this used a few times in other ways, but after each encounter where damage is suffered, if time is spent bandaging, washing, binding and cooling down, then half the damage can be healed. Round down. You know when you fall down the stairs or go over your mountainbike's handlebars, and although it hurts for a bit, after a few minutes rest or a nice cup of tea, it's a lot less painful and you can get on with your day.
So, for example, Kodak the Barbarian is 5th level and has 18 HP. He's hit by a crossbow bolt for 7 damage but survives and slays the lone goblin. Assuming he can rest, extract the bolt from his torso, and wash and bind the wound, he'd get 3 HP back. In a running battle where he can't take the time for this, such as fleeing the Sultan's Palace with the Princess over one shoulder, it doesn't work.
There's natural rest and recovery, which is 1 HP per day of rest. Rest can include training and exercising, but no real dangers or overexertion. Must have clean water and food for this to occur, though.
But there's a bit of variation in quality;
- Quality potions - deep translucent blue in colour, made painstakingly by really good alchemists that specialise, high level mages, and monks in temples that have a tradition and a secret recipe handed down through the years. Tastes like a fine liquor, and costs 300 Gold Pieces or more. Heals 7 HP if all is drunk, 3 if only half the bottle is consumed. Rather addictive if consumed too often...
- Average potions - lighter blue, almost turquoise, and cloudy, produced by standard alchemists (small batches made but many other potions also brewed at same time) and witches, with their strange ways - don't ask about the ingredients. Also the type found in ancient ruins, goblin loot and offered as rewards by cloaked men in taverns. Would fetch 100 - 150 gold in the right type of transactions - night markets, desperate adventurers (their normal state of existence), Elven nobles slumming it... A bit of variation in quality, so heals 1 - 6 HP per bottle, no half sips. Tastes like a half decent red wine, with a peppery aftertaste. Can only drink once a day; any additional produce cramps and no healing.
- Hedge potions - a very light blue, with little insoluble 'bits' floating in it. Frequently with a soapy foam on the surface. This is the type your average villager would be most common with, and is brewed using reasonably common herbs and fungi, probably including penicillin. Probably made by wise women/men that live alone in a hut in the woods, hermits, village herbalists, goblin shaman... The type found in goblin ruins and treasures. Can taste mind numbingly hot, intensely sour, nastily sweet or think and soapy. Not pleasant. Heals 1 - 4 HP, but can only be used once a week, otherwise something resembling a severe allergic reaction occurs. Also not pleasant. Still, it usually stops those suffering agricultural accidents from dying.
These healings can be tough on the body. Steven Erikson's Malazan Book of the Fallen series (if I remember properly) has magic healing quite nasty bodily wounds, but not healing the mind or spirit's response to the damage, which can't comprehend the sudden change. Rest helps, sometimes unconsciousness does too. The gods can lessen this impact, but sometimes don't, either due to benign negligence or, in some cases, because the injured needs to learn a lesson.
Either way, adventurers use the term "Health Struck" to describe the punch drunk, slightly disassociated from reality, unfocussed behaviour of those that have not reacted well to magical restoration. If this condition is seen in someone in dangerous environments, most parties would hole up until it passed, or even decamp back to base. Others would look forward to the amusement to be had.