Hi Sue
I had a Hycosy last week which is the same thing I think. It's an internal ultrasound which checks the uterus and ovaries, then dye is squirted through a catheter to check tube patency.
It's not the most dignified procedure to go through - hence I kept DH outside the room while it was being done!!
Good side to it is that you know the results straight away, down side, for me, was that it was very uncomfortable when the catheter was inserted. It's comparable to very bad period cramp, but it did go away within an hour of the procedure ending and I could've gone back to work, but DH had offered to look after me, so what can a girl do?!
It really wasn't that bad and I was very nervous going, but I know everything fine with both of us now, and my mind's a bit easier.
Incidently, it may be just coincidence, but period has been heavier this cycle, so be prepared!
Good luck and I hope it goes well for you!
P.s. take a sanitary towel with you - there can be abit a leakage afterwards!!