Panic attacks and pounding heart

You should see your doctor and get a physical, a cardiogram (don't freak, heart stuff at your age is pretty rare and usually easily treated), and a thyroid test. If nothing turns up, it might just be the way anxiety manifests itself in you. Tried breathing into a paper lunch sack? Used to be said that young people never got depressed or anxious but they do and good safe treatment is available, both medical and non-medical.