I guess when something occupies your mind as much as a wedding can, some thoughts can carry over to your subconcious. I have had some of the most weird wedding dreams where I freak out about something so bizarre that I can only shake my head upon waking up.
Most recently, my dreams included forgetting my veil and having to settle for something made out of leaves, my bouquet constantly falling apart, and everyone doing some sort of choreographed dance while I was walking down the aisle (don't even ask).
Once you wake up and realize it was not real, you can laugh about it, but I can't help feel a twinge of dread everytime I have one of those nightmares.
Have you ever had a nightmare about a big event? About your wedding? I'd love to hear it.