Help--woke up from sound sleep, extremely disturbed by dream...?

What causes such f8cked up dreams? My dream was nothing short of just that, not to mention morbid and extremely disturbing. I awoke from a sound sleep because of it and I would just like to know, what causes such messed up dreams? Why me? Why do they make me creeped out? Why not happy dreams!? Ughh..still cringing..