To start at the beginning - most colonoscopies show that there is not anything serious to worry about, the signs and symptoms are caused by something minor.
You don't need a special diet, the laxatives deal with your innards perfectly well. They are very efficient. Arm yourself with a soothing cream in case your behind gets sore, and don't plan any socialising for after you have taken the sachet(s). Don't wear your best fancy underwear either, you may regret it.
Someone has posted on the other thread a description of the colonoscopy she has just had. It sounds very like the one I had.
I don't remember anything of the actual procedure. I was planning to watch the monitor to see just what the inside of my sigmoid colon was like, even got into a comfortable position where I could see it clearly while still presenting a good target for the technical stuff.
Then suddenly I was in the recovery room and it was all over. The tiny tablet to relax my muscles had knocked me out completely. They had found nothing amiss in my sigmoid colon so had gone further to look higher up the system, but I knew nothing about it. I was told there was nothing wrong there either, immediately I was awake enough to listen.
I think they will be well aware if you need a bit more sedation, and will give it you before it gets unpleasant. The last thing they want is someone who is unhappy. I suspect that some of the horrendous reports on the net are by people in countries where you pay extra for the sedation/anaesthetic - and some are by people who have not even had a colonoscopy at all, but like the thought of describing one.
Dh drove me home, where I had a cuppa then went to bed for a while - I was quite sleepy. I had no after effects at all.