What does an anxiety attack feel like?

Today during this big testing process called Terra Nova testing, I don't know what happened, but i totally flipped out. We were on the last test of the program, mathematics computation, which is my least favorite subject. In the middle of the test, I started shaking uncontrollably, and sweating a lot. I began to have a headache. I felt lightheaded, and my stomach was upset. The kid sitting next to me was tapping his pencil on his desk, and I felt like SCREAMING at him to stop! I tried to calm myself down, but it didnt work. I got really worried that I would fail miserably, so i kept filling out the answer sheet. I finished the test and I asked my homeroom teacher to call my dad, because i didnt feel good. It was the worst feeling of my life. What was this?