This is an interesting article about cardiologists dealing with patients who have Atrial Fibrillation. They say that as well as the heart condition, patients may also develop anxiety which can cause similar symptoms. A panic attack can bring on Atrial Fibrillation and vice versa.
The study also points out that many with anxiety overestimate how many times they have Atrial Fibrillation. This is hardly a surprise for two reasons. One is that anxiety can magnify other things as well. It is part of the disorder. The other problem is that if the symptoms are so similar, how can they tell?
It does mention trying to measure their pulse and use Yoga. Both of these have apparently had good results.