I've had two of these, and various other bits of 'mucking about' over the past three years. As everybody else has said, Gordie, this is not anything to worry about. The worst thing about it is the 'cleansing' process and that's much less explosive than it used to be.
Really, the worst thing on the day is the feeling of lack of dignity. The staff will be well aware of how you feel and will do everything in their power to make it seem as normal as possible.
They will give you all the relaxation medication you need, they'll ask you if you're still feeling anxious and will respond accordingly with more drugs, if necessary. You will not be allowed to go home on your own afterwards as a result of the drugs.
You'll be able to watch what's going on on screen if you wish. But you don't have to. I've always found it fascinating, I must confess. It's an everday job for the people who are doing it, you won't suffer, believe me.
And your final line is the most important thing. If there's any possibility of anything nasty up there, it's better to get it dealt with as soon as possible.
Good luck, and post on here to let us know how you got on.