I peeked at a few information sites and most seem to describe acute band slippage symptoms as pain, bloating, vomiting or difficulty in swallowing liquids and solids.
I also read that a band can sometimes slip only a little, in which case the problem may be fairly easy to fix. The important thing is for you to seek professional advice, fast. It might be a different problem altogether!
Good luck and let us know how you get on x