I need to lose some weight FAST- but how?

I'm not exactly a small girl (though I'm not grossly obese) but I'd like to not embarr myself in the somewhat skimpy halloween costume I'm wearing to a really big party. So losing anywhere from 10-20 pounds in a week and a half would be perfect. I've seen them do it on Biggest Loser and other shows, and I know its not the healthiest thing, but I'm desperate. Help! I don't mind if it is crazy, but no mean comments people.