I had a dance performance last night, and, like everyone in the company, I went through my same old performance ritual: watch the clock carefully, and fifteen minutes before going on, dash to the bathroom to pee. And, as with every performance, right before we went on, I really really felt like going, again, even though I knew my bladder was empty....
And this morning, I wondered: why? I mean, yeah, "flight-or-fight response," but, physically, why? Emptying one's bladder to flee the enemy makes sense, but if I already did that, why is the feeling still there?
Part of the answer, according to the internets, is that stress makes your (usually relaxed when empty) bladder muscles contract, and elevates your blood pressure, which also puts pressure on the bladder. Both of these things fool your brain into thinking you need to pee, even when you don't --- and if you get this same urge before a big public speaking or performance gig, now you know why.
The dance performance went great, by the way.