Bunnicula-
I had that happen to me only once before, I had to take the hose outside and run water through it to clear it! The hose that you are using, is it a very long one? My shop vac came with a short hose and a long hose and I clogged up the long hose. I think its because it has such a long way to travel so it loses a little bit of suction. I've since switched to the shorter hose and haven't had a problem!
My dream is to some day meet the man of my dreams, and own a Dyson -- and maybe not in that particular order, either.