I've had 2 hysteroscopies, both with polyp removal.
Both times were painful, on and off, it wasn't a continuous pain, but I just gritted my teeth and stuck it out. I was told both times, that if it was too painful I would have to have a ga, so it can be done in the nhs.
Afterwards you can have bleeding and period like pains, and if you have polyp removal you can also experience contractions, but these after pains are short lived and will have stopped before you leave the hospital.
I did take paracetamol beforehand to help with with the pain. On my second visit I was told I could have taken both paracetamol and ibuprofen.
There was a lady who put on here, not that long ago, how easy and relatively pain free hers was. So it all depends on each individual.
What about taking paracetamol and ibuprofen (if you can), and try it, and if you really cannot cope then chose to have the ga then.
I'm not sure how ling before the procedure you need to take the pain killers, but it will be in your information leaflet you are given.