As you get older you don't want to just do the same thing, otherwise there's not much point. I think it's more or less trying to write things that, perhaps, say more by doing less, or you're always trying to refine things, make things a little simpler, a little more essential.
Really, a nightmare just really has to evoke some sort of, we call it, dysphoric emotion or something uncomfortable. You could be sad, you could be unhappy; you could be scared, anxious. But traditionally, the definition is you have to awaken from this nightmare.