Hello there!
I actually had a fistulagram done a few weeks ago. Its not all that big of a deal, people get it done all the time. I normally go once a year sometimes more if I'm having issues with my fistula since it was placed. (had my fistula almost 7/yrs & no major issues yet)
You normally don't feel anything other the a little pressure during the procedure, unless they have to do angioplasty & open your fistula up slightly with a balloon. In that case my doctor always gives a little relaxing medicine so it wont feel so sore. Honestly it doesn't hurt though !! Just a little discomfort if they have to use a balloon.
Good Luck
~ Marna