Well, this may not be what you want to hear, but my HSG was horrible. I went into mild shock from the pain and had horrible cramping, nausea, sweats, chills, shaking uncontrollably and finally diarrhea (in the bathroom, not on the table haha). I was there for 2.5 hours past the time I expected to be there, recovering in an empty exam room.
BUT, mine was horrible because I had blockages in both tubes. Because of the type of HSG that was performed (sterile water with live u/s monitoring vs. dye and xrays) my dr asked me when we determined that both tubes were blocked if I wanted her to try to open them right then by slightly increasing the water pressure. Since DH and I had decided against surgery if the blockages were permanent I told her to try it. It was when she increased the pressure that the pain was greatest. My left tube cleared within a minute, she turned up the pressure again - the world started spinning and I thought I was going to throw up. The right tube cleared and I felt better but not great.
The good news is, because we were able to clear the blockages our daughter was conceived 8 days later. For me it was painful, but sooooooo sooooooo worth it. I would do it all over again to have this precious baby.
My suggestion would be to take someone with you in case you do have a bad reaction to the procedure. I didn't have anyone with me so I had to wait until I was confident in driving myself home. Also, make sure you take Motrin or Aleve 30 mins before - I forgot to do that and it may not have been that bad if I had remembered!