You probably weren't bitten, but stung. As the name suggests, bristleworms are covered in tiny, sharp porcupine-like bristles that will stick you..... some much more painful than others. If you have bristleworms in your tank, you want to wear something like mechanics gloves while in there.
There's nothing wrong with bristleworms in your tank..... they can be very beneficial members of your clean up crew. There are only a few out of a thousand+ species that are bad. If they get too big, just remove them with a trap or large forceps.