Actually, there are two versions of the restoration spell, both of them are Clerical in nature, however.
Lesser Restoration is a lower level Cleric spell (4th or 5th level I think?) that only restores levels drained.
Greater Restoration is a high level Cleric spell (I'm not even sure that it is available for Clerics to memorize) that restores all lost levels as well as all lost hit points. This is what temples will cast and it is also what is on restoration scrolls that you will find and purchase throughout the game.
The bad thing about either of these spells is that it makes the caster very tired. They will almost always start whining about how tired they are and how they need to rest fairly soon after casting the spell. Hope that helps!
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My *God* man...would you *please* eat something!?