I have had a number of sigmoidoscopies and colonoscopies and found them terribly painful. As I have to have them on a regular basis, my gastro consultant put me on the 'anaesthetist supported list' for my latest one. It was a doddle, no feeling of going under (it was deep sedation rather than an anaesthetic) and no feeling of coming round, and no recollection of the procedure.
I would suggest that the patient makes their fears known to the consultant who will take it on board and make the necessary arrangements.
There is a vast difference between sedation, and anaesthetist supported sedation. I have no fears about having any further procedures providing they are done under anaesthetist supported sedation. I would refuse if this wasn't available.