In my physiology class, we talked about how sometimes you have to reset your circadian (sp) rythem thingy....like what nacht was sayin I think; one way to do it is to go to bed at like 4pm, get up at 11am (8hrs) then the next day got to bed at 5, get up at ten...and so on until you are on a normal sleep schedule;
also, make sure the temp is comfortable, no tv, no lights...can't remember what else messes up that cycle.

nightmares though...check how you are handling stress and life events..do you have a good outlet? That's justa theory...your excess worries are bing dealt with in sleep, but I am not knowing. I know people who are being badly triggered can also have nightmares.

Take care,
-kayo