I recently had the test and there's not much to it. It takes 4-5 hours because of the wait time while waiting for the drug to circulate through your system.
The techs will set up an IV through which they inject the trace medicine.. bring your own snacks, the hospital didn't supply any but they make that clear at the start..
In a nut shell they follow the blood trail to the heart then through the heart at the end to determine if there are blockages the they apply an antidote to offset any side effects of the medicine. You feel a warming effect slightly from the medicine. Whatever side effects if any you may have disappears immediately with the antidote.
I'm sure you have nothing to fear form the test..
Hope this eases your mind.. best if luck..