I've only had a few HP dreams that I can recall and none too clearly. Many lovely Weasley boys and a Hermione/Neville matchup that was rather sweet.
Buffy was the Dream Fandom for me. It seemed I was always joining the gang for some adventure. Sometimes I was Buffy, but mostly I was me, only I was *cooler* than Buffy. Yeah. Hmm. Usually these dreams contained the awareness that Buffy was a TV show, which was pretty nifty.
One time Xander, Jonathan, and I had been called down to the mall to investigate some supernatural occurrence. But when we got there, nothing was happening. I said to Xander, "I'm getting worried. We're already twenty minutes into the episode and there hasn't been a fight scene yet."
But the best Buffy dream of all was the one where I was helping Jonathan move and we took a break and sat down on a couch together, one at each end with our legs stretched out to tickle each other's toes, and he asked me to beta-read a long Han/Luke slash story he had written. I said yes. But I never got to read it.
I often wonder what it would have been like.