I've had two discograms (both with sedation) and both were different experiences. The first I don't really remember much at all and it was positive at 2 levels. The second I remember very clearly and it was positive at 3 levels. Will your doctor be using any sedation for you? Some doctors do it with the patient completely awake and others use versed and put you in a "twighlight"

- not completely awake and not completely asleep.

You have to be awake enough to talk to them and be able to answer questions
Everyone is different with pain afterwards.

If the test is negative you won't have any pain after. But if it's positive you could have some increase in your normal pain - this can last from a couple of days up to a couple of weeks. One of the best ways to get yourself feeling better is to drink as much fluids as you possibly can. The more you drink the more you'll flush the dye out of your system and this is what is causing the increase in pain. I also found putting ice on the area to be helpful.
Hope this helps and Hope things go well!