Hello! yes, i've had two saline sonograms! the first was i cramped pretty good, but my RE said they must have pushed the saline too fast, also i had never been pregnant at that time.. the second time, when my RE did it, it was totally painless, and as isabelle said, i went right back to work.. it will make sure that you have no fibroids, septums, etc in your uterus! GOOD LUCK! : )
I'm not sure if hysterogram is the same as hysterosalpyngogram (HSG) which is the dye test to see if uterus and tubes are ok... I did it a year ago, it took about 10 minutes, was uncomfortable but not super painful and I went right back to work 30 minutes later (got it on my lunch break). It was a useful test in my case because it revealed that I only had one functionning tube, which is why I wasn't getting pregnant.
I hope this helps! Good luck!