Being checked for cholecystitis. Abdominal pain, nausea. Ct scan clear. Urine suddenly brown. Worry?

Maybe. Notify MD. Liver disorders can cause dark urine. Discolored urine can also be caused by certain foods, medication, and kidney infections. Also if you haven't been hydrating due to nausea, the next urine may come out darker than usual. The bottom line is, your physician should know about this so he/she can run more tests and get a better idea of what might be going on.
Tell Your Doctor. Any changes in urine color that have no distinct dietary association, reoccur or last longer than a couple days should be reported to a physician for assessment. Symptoms like abdominal pain and a sudden change in urine color to red or brown could prompt investigation into problems with the muscles, kidneys or liver as well as issues like porphyrias. Inform your physician of symptoms.
Yes. See your doctor, need urinalysis and blood work. Often liver products show up in urine, ask if you need a hida scan to check gallbladder function, pain is telling you something is wrong so get it checked out immediately.