Hi there, I had a HIDA scan a couple of months ago. It's really no problem. They shoot you up with two different fluids, one is radioactive. You lay on the table and they watch your GB for a while. Then they put in the second fluid, which is to empty the GB and they watch you a while longer. Mostly it's pretty boring. My stomach got queasy and crampy when they shot me up with the second chemical. The whole process took a while, like about 2 hours.
Have you had an ultrasound on your gallbladder to check for stones? I had one and showed nothing, then they sent me for the HIDA scan. That was normal. I've been having IBS-type diarrhea and gas problems, and right now am taking Aciphex for reflux. I may have a duodenal ulcer. I have not had a gallbladder attack (or even close), just mild pain in the area of the GB, which may be the ulcer. The reflux meds are helping, but I may have a bit of a problem ulcer because my issues aren't gone entirely. Next up would be the endoscope and a colonoscopy for what may be a separate issue.