I have had a few flex sigs. The first I did with local anesthesia, because I read some horror stories from those who did the procedure without. However, I have done several others without meds, and it wasn't bad at all. A bit uncomfortable, but manageable. Granted, I assume if you have a lot of active disease it could be a bit more painful. But I wouldn't stress over it. It's only takes a few minutes.
Good luck and let us know how it goes on Friday!