How can I not be nervous for tomorrow's performance?

I have a clarinet performance tomorrow and I'm always so nervous. The last time I had it I felt like I was going to have a heart attack and I was hyperventilating and I could feel my heart beat so fast!!! I felt like I was going to die! And when I actually got up to perform my hands were shaking so much and my notes were so shaky it sounded bad. Help?!