Shropshireless, I've had hysteroscopies on 3 occasions over the years. First, in fertile years, was under GA, but only because the procedure was combined with laparoscopy & D&C, the next also premenopause, was with light sedation (conscious but relaxed) & local anaesthetic to numb the cervix. The last - several years postmenopause with poorly controlled VA - was without any pain relief or sedation. I was instructed to take 2 paracetamol an hour beforehand which I did, but felt no benefit from them.
The 2nd procedure, with light sedation & local anaesthetic was the least complicated (none of the after effects of GA) & caused me no problems either at the time or afterwards. I was pleasantly chilled, able to watch what they were doing on the monitor & felt no pain. But (not sure where you are in the transition) that was before I had VA so tissues were robust. An anaesthetist was standing by to put me out if necessary but there was no need.
As others have said, the procedure is over in a few minutes & it may be that without any sedation or pain relief you would find it more bearable than you fear, but like you I find smears really difficult these days & like CLKD, Taz & Nik, would recommend you ring & ask in advance for light sedation with local anaesthetic if you are at all anxious & this has not already been offered. It's in their interests as well as yours, that you are relaxed on the day.
Many of us have had this procedure when bleeding has to be investigated & it's worth it for the peace of mind, so if the hospital advises it I would agree to it. I completely understand your apprehension, but it will be over quickly & you will get through it.

P.S. Was posting at same time as Katejo! If unlike me you are OK with GA, I would agree that's probably also a better option than having hysteroscopy without any sedation or pain relief, but I remember on past threads that other members have not found GA or even light sedation necessary. I think variation in how comfortable we find it probably depends upon individual anatomy, whether VA is present, the skill of the practitioner, past bad experiences with smears etc & how anxious we are on the day.