Even though in our society we try to squelch it with meditation or medication, the stress response is really a practical one. What if a lion were chasing you, a good strong adrenaline rush would be just what you needed to escape. Pity the human who is dull and slow to respond to this sharp toothed stimuli.
Stress is similar to allergies in the sense that it is an overreaction to something benign. And since I have a hearty helping of both anxiety and allergies, I know that it is not pleasant to endure a rash of violent sneezes or a heart pounding and hand quivering moment. But it means that your system, be it immune or nervous, is working and is so sensitive that it can sense a pebble in the shoe of the person next to you.
I know that anxiety and stress can be paralyzing, I know it very well actually, but in the right amount it can be a catalyst to progress. Think of the paper you wrote that took all night and had you pacing the room after each paragraph, but then something good emerged. Think of the speech you gave that turned out well. Think of the stress you were under in the interview that was a success, or the day that you aced the SATs. They were all stressful times, but you rode the wave of adrenaline right into the drivers seat of your life. Without that push, where would you be? A lions lunch perhaps.