It seems common sense to state that stress is something which is negative. After all, we tend to avoid stressful situations, and being under stress isn't something we naturally enjoy.
However, there are actually several ways in which the body can respond to stressful circumstances, and some of them might be surprisingly useful. Psychologist Kelly McGonigal posits the idea that if you feel challenged when stress takes hold, it can actually help you shift into a state wherein the body has increased blood-flow to both your muscles and brain. This, in turn, allows the brain to pay better attention to everything in your environment, which is better than the tunnel vision experienced in a fight or flight response. To be terse, you're basically smarter with a challenge response to stress.
So, in the future, don't become anxious when you see your sweat, and don't try to calm down when your heart beats faster. View your stress as a resources, see the stressful event as a challenge, and you will enter a state which is superior.