Ooooo! I've had that dream before. It's in the same family of dreams I used to have when performing theatre (forgot my costume, props, lines, you name it) or studying for an exam at school (forgot EVERYTHING I knew about subject, test wasn't written in English, MY test was blank). I think it's just that you're excited/nervous/pre-occupied with Hallowe'en...and it probably means you'll do a spectacular job. I always noticed that when I had one of those dreams, it made me MORE prepared and I always got the extra details done, really studied my lines, remembered every article possible (and thought of new ones) or studied like I'd never done before and aced the test.