nausea after surgery!
Have you contacted your doctor? I don't want to scare you, but one of the symptoms of a band slipping is nausea. If you haven't already done so, I would call your doctor to see what he/she says.
I had the dry heaves in recovery and right after surgery, but that's it. I haven't been nausiated one time since. It could very well be the foods that you're eating, but since it also happens when you haven't eaten anything I would seek advice from the doctor.