 When people are entering into a state of high performance anxiety, we feel our heart rate going up. The blood pressure will be going up. Heart rate variability goes down. Blood is pumping to big muscle groups because we are getting to a state of being ready to fight or to fly. And what that means with the blood leaving the core into those big muscle groups is that we get a sense of butterflies that we experience in the stomach. I used to want to throw up when I was nervous.