Hi, I have had lots of cystoscopies in my life! I have a lot of coinciding medical conditions, and completely understand your need to be under general! I've had several, and I mean a lot, of surgeries, so I am very familiar with the process before, during, and after! It's easier to explain the details in a private message, so feel free to send me one, but in a nutshell, I would tell your nurse all of your concerns before surgery. You can also speak with anesthesia about what will and won't work for you. If you make an appointment to speak with a nurse in anesthesia before hand, they can put notes in your chart, so everyone is aware of your needs on the day of surgery! In my experience, the more you tell them, the better!
Just to answer one of your questions though, they can do all the positioning once you're asleep. That's what they do for me because I can't position myself for physical reasons. If you have any other specific concerns, please message me, and I will be glad to provide you with whatever information I can! Lastly, I just want to make sure you know that the anxiety you're feeling is completely normal before surgery! I've had 21 of them, and I still get anxious every time I go under anesthesia! I would be a little concerned if you weren't at least a little bit anxious!