Here's the scene. The audience is waiting with bated breath, you're just about to give a speech, and suddenly you notice your mouth is dry as sawdust. You haven't said a word yet! Why did you get cottonmouth before you even began?
Fight or Flight
The dry mouth that, for many people, goes along with public speaking or performance is connected to the "fight or flight" response. When you're nervous or afraid, the nervous system slows down all the body processes that aren't necessary for your immediate survival, and amps up the ones that just might save your life-that is, if you're about to be attacked by a predator like a tiger or a bear.
As the "fight or flight" response kicks in, your heart rate goes up and more blood goes to your heart and major muscle groups, so you can make a quick getaway, or grab a big stick.
When the "fight or flight" response is in full swing, digestion comes to a standstill, because who cares about breakfast when you're looking into a tiger's mouth? The salivary glands in your mouth are part of your digestive system, so they too go through a temporary slowdown, producing little or no saliva. That's what makes your mouth feel dry. You might also feel butterflies in your stomach as digestion comes to a halt.
Cottonmouth, a pounding heart, and butterflies in the stomach can be a hassle, but there are some advantages to activation of the fight or flight response. You may feel more alert and energetic than usual, lending your performance a memorable flair.
"The Last Word." The New Scientist.