I have these regularly - I guess I've had more than twenty over many years. Yes, the worst thing is the bowel preparation day. Do follow the diet guidelines and don't worry too much about hunger - after you start taking the medicine your appetite vanishes. I have found that the only thing that works for me is three sachets of Picolax, and I usually have to kick up a fuss to get the third prescribed.
If you're a novice, then the procedure should be no worse than uncomfortable, though I have found that the whole thing gets more bothersome the more that I have had done. I would recommend opting for the sedative - and I now often need gas and air as well. You will be able to watch the whole procedure on a screen, and in practice you can hardly avoid it. These days they don't give you enough sedative to knock you out completely (this is a good thing) They may find one or more polyps, which can be removed during the procedure. Sometimes they may find worse, and the doctor or nurse practitioner will talk to you about this afterwards. This is why it is really important to have someone to collect you, as the effects of the sedative make it difficult to take everything in, and you need a second pair of ears.
Now that you are "in the system", you should think of this as a very good thing, as I do. My tendency to get colon cancer has been kept virtually trouble free and in the background for over 25 years now. Hopefully, you will be as fortunate.