One of my friends used to be ADAMANT that you're "supposed to" brush your teeth as soon as you get up. I wonder if she still feels that way...
I refuse. I'm not about to brush my teeth, then eat and get my mouth all nasty again. Totally defeats the purpose. On weekends, I sometimes don't brush my teeth until the afternoon because I usually sleep late enough that I have to have two meals within a couple of hours before the gym. I wait until I have eaten both, then I brush. Oddly enough, even though I end up brushing them later in the day, I tend to brush them three times instead of two more often on the weekend than during the week.
If you don't want to go back upstairs, why not just keep a spare toothbrush and toothpaste downstairs? There is no rule that you're only allowed one lol