Palpitations are very, very common for those of us who have anxiety/panic. They can be frightening, but 99% of the time they are totally benign.
Are you being treated by a doctor for your anxiety? If not, I would suggest you start there and discuss your heart palps with him/her. They may recommend you see a cardiologist to rule out anything organically wrong with your heart. It would be my totally non-medical opinion that since the palpitations decrease with exercise and yoga, both of which relax you, than the cause is most likely anxiety. But I am NOT a doctor and that is only my opinion!
You ask how you can overcome incidents from your past. The best, and sometimes, the only way, is through therapy.
Peace
Greenlydia