Just relax! Your blood pressure will be way up if you are nervous and have a case of "white coat syndrome"....I read the comments about pee too although I don't think it makes that much difference - if you have kidney trouble or blood in your urine they will spot it.
..oh, and seeing as you're paying a king's ransom for being there, read ALL the magazines, drink as much free coffee and water as your body can hold and of they have any free biscuits or anything there.......well, just go for it.....