Yes, I have had this twice.
If they offer sedation then take it and you will not be aware of much, although I do remember occasionally looking at the screen a thinking “that’s me”!
No pain or discomfort. Quick recovery and they give you the results immediately.
Worst bit for me was the bowl prep. What made it easier was chilling it, adding some lime cordial, and using 2 straws to get it past most of the taste buds on your tongue. Also having plain very cold water to swish mouth with and spit out after each drink of the stuff. (Don’t swallow the water as you have to take so much fluid in anyway). However, I am a total wuss with anything I don’t like the taste of.
Stay near the loo and have Vaseline to sooth if needed.
Good luck x