First Time - Nervous!

I'm having my first colonoscopy and I'm extremely nervous about the cleansing procedure. I have constipation so I'm afraid that will make it even worse. I'm not evne sure if they are going to have me do an enema at home or if they will want to do it at the hospital. That's what make me nervous. I've read that sometimes you can't hold it so I'm imagining me behind in one of those curtained partitions getting the enema and then having to eject it into a bedpad while the nurse holds it and watches and 20 people are outside the curtain listening to what's going on. I know that they do this all the time, but I DON'T. Can they do the enema while you're in the 'twilight' mdoe, or do you have to be totally awake for that? Thanks much.