When you are low on health, go to a mushroom ring and save your game. Then, quit the game and load your saved game and you will now have full health.
Get the light rune in chapter 3 and equip it. If your in a big battle and get that warning sigh from your orb then run away until the monsters gone then start the runes power and wait there till your health is full. Then go back and kill the rest of them.
NOTE: kill the spawners first the go kill the one that are still there
Various Rune Locations
Light Rune- Go to Chapter 3 and a witch and her sister will give you the rune and a spell.
Fire Rune- Go to Chapter 4 and defeat the Beguiler and his clown to get the rune.
Water Rune- Go to Chapter 8 and reunite the lost brothers to get the rune.
Dark Rune- Go to Chapter 10 and reunite the two children with their mother to get the rune.