As others have said, the worst part is the preparation because the stuff you have to drink, and there is quite a lot of it, tastes awful, but you are doing that part at home so that makes it easier.
some tips, put the jug of preparation in the fridge , it tastes marginally better when cold. Have some Vaseline handy for your bottom because it is going to be working overtime! Make sure your loo is warm, wear loose clothing and tell the rest of the family you have priority. It is not like having a bad dose of the runs, you will have been on a bland diet and have fasted so what comes out of you is not too unpleasant .
If you start taking the picolax stuff (or whatever they give you, might be a different name) at about six in the evening then everything will be more or less done and dusted by about 11 o'clock so you can get a decent nights sleep, you won't be up and down all night., but sleep on a towel in case of a drop of leakage.
During the procedure there is less of you on show than when you have a smear so don't feel embarrassed. The worst bit is the paper knickers with a hole! It is not painful though you might feel a bit of pushing at the last bit as it goes around, hang on for that, it's important they are as thorough as possible. Some people don't want to look, but I watched the screen and found it quite interesting through my Valium daze.
you will probably be very farty for the rest of the day.
Don't worry, as procedures go it is ok,I am sure there are worse, and it is a very effective and quick way of diagnosis. If they find polyps or anything suspicious they nip them out at the time or take a biopsy and send them for analysis, you won't feel the nipping btw.