Hi Ladies, my hsg was a little while ago now but from what I remember it wasn't too painful just felt a bit crampy but it was over before I knew it. Take some paracetamol before you go in, it helps a little.
They use a speculum, just like a smear, then put a catheter in your cervix for the dye. You will feel some pressure but for me it was no worse then some period cramps.
I had a nurse let me squeeze her hand throughout if needed and she was chatting away to me to help me relax. She was very lovely and made the whole thing so much easier as I really don't like hospitals/medically things!