They insert dye into your tubes, it's a little uncomfortable and your dignity goes out of the window but it's not really that bad. But I had really, really bad period type cramps afterwards, the type where I was crying and rocking back and forwards. I didn't take any paracetamol beforehand though and had to wait for them to kick in until the pain went away. I was fine when they did start working though. Make sure you get someone else to drive though as I drove myself home (only a 10 minute journey) and it was a bit much what with the cramps.