mine hurt like HELL, but that's b/c my problem was a 9-10.
to better explain, the discogram seems to mimic you maximum pain. so if you normally experience pain at the 4-5 level, then that's what you'll feel. if your disc is normal (they'll inject normal discs for comparison purposes). since my annular tear was a 9-10 at my worst, that's what i felt. of course, the disc appeared "normal" in all 5 mris, so it was probably the shock value that added to the pain!
again, just my personal experience...others have very different experiences. but if they don't know what's causing your back pain, and mris, etc. haven't found anything, then it's definitely worth it.
keep us posted!