would any of them happen to involve riku training him to the bone--i mean

I'd like to say that once nightmares are eaten/cuddled away, they won't return unless it's a recurring dream--this is up to the player, though. They'll also, of course, get happy dreams in place of their nightmares. People who participate in a personal cleansing (I need a better term for this, it sounds. Weird.) will probably have much longer effects, though, and that's on a case-by-case basis!