I have had two. Both times were okay.
The first time, I made my husband take me as I had read horror stories on the interwebs. Its quite a drive to the RE's office, so I didn't want to be stranded there if I was unable to drive home. I was super anxious. I took motrin prior to the test. But really, it wasn't that bad. I mean, don't get me wrong, I am not a fan of the speculum... My RE numbs the cervix, so I didn't even feel them putting in the catheter. It's awkward. My right tube didn't spill. But I have definitely had ultrasounds that were way worse than the HSG.
The second time, I drove myself. Took motrin. Wasn't anxious. Right tube still didn't spill (surgery revealed it was kinked and adhered to my large intestine), but the test still wasn't bad.
Good luck to you. I will say to take your own pad. I didn't need anything heavy and I certainly didn't want to wear that brick of a pad the hospital offers you.