Just a quick question, I was wondering if there's any way of creating your own dream, before you fall asleep.

For example:
I just rode a rollercoaster, it was fun, I want to do it again. That night I (insert strategy (if one exists) here) and dreamed about it.

Of course, I have no idea if this is possible, I have tried just visualizing it a couple times in my mind, then going to sleep, but that usually results in unwanted backwash dreams. IE: Dreamscapes that have a couple basic things in common, yet don't share much beyond that.

So I'm asking you. Is this possible (give sciencey proof if needed) and if so, how do I do it.

Sweet dreams.