The prep is not so bad really, as long as you are prepared. I didn't throw up at all, just ran to the loo a lot, think mils attack. The stuff tastes like Andrews- you know the powder stuff your Mum used to give you when you were little and had a sore tummy, gassy.
I thought that it would be a lot worse, although I think that subconsciously I ate a lot less in the days coming up to it so there wasn't a huge amount to come out. I drank chicken bovril and 7up on the day, I was only allowed drink clear liquids though so coke wasn't an option.
When is your appointment for? This IS a good idea. We're here to reassure you.