I also had to have a hidascan...along with the slu of other tests. (ugh!) Anyway, a hidascan, I believe, tests the FUNCTION of the gallbladder. It just doesn't look for gallstones. The test took a couple of hours and it's not very comfortable, but not untollerable.
Hmm...an endoscopy and CT scan are probably good ideas because of your urinary symptoms and history of cysts, but you should also get a report of that ultrasound you had done in the ER. I'd be really, really surprised if they found you indeed had gallstones and didn't recommend removing your gallbladder quickly. Do you have the report handy, by any chance?
There is a method called ERCP that they use to essentially dissolve stones if they become lodged in the bile duct, but the preferred method is overwhelmingly removal of the gallbladder.
The CT scan will also show gallstones, it's just a lot more expensive than an ultrasound and exposes you to a lot more radiation...but, like I said, it's probably worth it given your other symptoms that are not so readily explained simply by gallstones.
Good luck and let us know how your tests go!