I had a flexible sigmoidoscopy a few years ago.
Never offered sedation.
Used the bowel prep kit in the morning, thought it hadn’t worked as I was expecting it to be like the enema I had in childbirth, but nothing like that. And they told me my bowel was lovely and clean.
As for the procedure, it was ok. I watched it on the screen, just a bit uncomfortable a time or two, but not a problem.
The results were nothing sinister, just piles, which I knew I had. It said I had good tolerance to the procedure.
Hope all goes well.