ALEXANDRA KOPKO WAS 11 years old when she experienced her first panic attack. Her heart fluttered and then raced. She felt pins and needles in her left arm, and her breathing sped up to the point that she felt light-headed. She was sure she was having a heart attack, which she’d learned about in a CPR class at school. Her mother, a teacher, recognized what was really happening and helped her calm down by breathing into a paper bag.