That must really annoy you. And scare you. I have a solution(i think). Before you go to sleep, take about 10 mins concentrating on what you want to dream about. Then, when you fall asleep, even if you don't dream about what you were thinking about, you should be able to manipulate the dream. If u can't, I'd suggest going to a shrink. K?

--Mr. Fluffy Pants
"Duck Tape is kinda like the Force - it holds the universe together."