Nightmares and stress

Lately, I have been having nightmares involving people I have not seen for a long time. I don't know what is causing it. I haven't been eating or drinking before bed or anything. Actually I believe that all those causes for nightmares are stupid. I think you get nightmares because you put yourself under a lot of stress. Strange because I should be under less stress lately. But as success slowly comes my way, I find that I can find more things to worry about.