Really, there's nothing to worry about.

When I had mine, I had to lay back on a treatment table, only there were foam blocks placed on the table, so that my hoohaa was actually at eye level for the radiologist LOL, and my legs were hanging over the side. First they placed a speculum inside, just like a pap smear, then threaded a thin catheter (tube) through the cervix, and then pumped the dye through the catheter. Then they inserted a long thin ultrasound into my vagina as well (there wasn't much room left in there after that LOL) to take pictures of the dye going through my tubes.

I had mild cramping afterwards, sort of like an AF cramp, but nothing serious. They made me lie down for a half hour, just to check that I was OK, then sent me on my merry way.

You'll be fine ... the pain, if any, is minimal. I was told to take 2 nurofen the night before, and then 2 neurofen the morning of the HSG in preparation, which I think helped. Good luck