I actually too have heard it's created in the stomach (I personally do not believe this, but I have heard it somewhere). Wherever it is created though, how are we to tell whether or not it's what makes dreams?
There just isn't enough research about it to say for sure. I read someone on Nexus mention it had an effect on how they felt when they'd wake up in the morning, but I don't want to misquote him so take that vaguely, but as far as I know I don't think it effects sleep patterns. Maybe some people with experience could fill us in on their experiences?
I'm curious about this too, good question BenevolentSon.