What causes disturbing nightmares?

I want to become a director, some scenes of my films though I want to be utterly disturbing and well detailed visions of just absolute petrifying shock. I've been having chocolate in the very late evenings before going to bed and I record my dreams in the mornings. Alongside I try to just simply get on my creative side to help my creativity in general, even if it's a happy dream. I want to direct science fictions and mysteries. What else can help me get creative dreams or nightmares before going to bed?