I think sleep is another factor in your last few days before a show that plays a major role that most guys don't really understand the significance of. I'll be the first to say its not easy to sleep before the show, especially the night before when your all tanned up and thirsty, but getting a great nights sleep those finally few days makes the biggest difference!
I think another thing guys don't really understand is the difference between 'looking' tight and dry under the lights as opposed to 'feeling' like your full and pumped after a workout. Lots of guys say they felt so much fuller and better the day after, and thats generally because they have re introduced water and the muscles are gobbling it up, but a lot of times when you look in the mirror that day after and feel like you could have won the show if it was right now, you're generally not going to show well under lights on stage, as they really do wash you out and the water making you feel full and pumped is really washing away the cuts that separate the muscles. At least that has been my experience with a few of the guys Ive worked with..
The whole last week is such a mind fuck man, I'll bet the stress hormones going off like crazy during that time screws with your water balance as well. I think most guys who recall doing any shows, don't have this energetic happy feeling when they remember they way they felt, its generally, very tired, stressed out, thirsty, and anxiety ridden.. Makes ya wonder how much better control you would have over your body if you were at ease in the mind...