I was having episodes of hyperthyroidism so I too had the uptake and scan. Let me tell you at the time I had it done, everything other than air was giving me side effects (even most food). My thyroid took in a lot of iodine. I had NO side effects. My goiter felt a slight bit bigger than usual, but it wasn't bad. I didn't have any restrictions. I went in, drank the radioactive liquid and a shot, and had some pictures done. The next day they took more pics and that was it. It was very easy. I was having a lot of problems with heart racing at the time, and it didn't make my heart race at all. I even went alone. Good Luck on the procedure.
I was diagnosed with Graves Disease and had a uptake scan and a ultrasound. The uptake scan was conducted in the nuclear dept. It required that I fast for 8 hours. I arrived at the hospital at 8:30am. Some measurements of my neck, thyroid was done! Then I was asked to take the iodine pill. There is NO side effect whatsoever. I can't stress that enough. I am a person who can feel when a baby aspirin is in my system, lol. After I took the pill, I was able to leave and come back after 6 hours. I was told that I could eat after 3 hours. I returned 6 hours later and pictures were taken for apprx. 25 minutes. no discomfort at all.
The next morning I had to go back to the hospital for additional measuring that took 5 minutes. I was told that this test is relevant to determine how much of the iodine was still absorbed in my thyroid within 24 hours.
I hope this helps.