I offer these observations in the same spirit as my pneumonia post: readers, Googlers and other web-surfers should be getting the bulk of their info from more authoritative sources. But if I could send a note to my former inexperienced self, this is what it would say:
(1) The 24 hour period leading up to the procedure is going to be more grueling than the procedure itself.
(2) The day before, drink lots of water right up to midnight. I mean it. I know you think you're drinking lots of water, but you're not.
(3) As soon as you've finished reading this, get on the phone and change your appointment to first thing in the morning. If you go ahead and try to put in a full day at the job before you're driven to the clinic, you will live to think of it as one of the dumbest stunts you've pulled in mid-life.
That's about it, really. Oh, and stop fretting: the doctor is going to give you an "all clear -- book another appointment 8-10 years from now."