If all your previous exams show no heart disease then yes they are benign and you can test all you want and the results should be the same. Once you develop your old routine your anxiety should abate. It took me a awhile to "ignore" them.
So these are probally benign pvcs or pacs??
"You get episodes of palpitations once a day that last for ten minutes." Lucky you!
Slowly start exercising/running again. Once you gain confidence that these activities will not provoke palpitations then you can begin to return to your normal routine. The check for Hypothroidism is a quick blood test and symptoms of it don't occur every day for ten minutes. Your looking for problems that don't exist.
The hyperthroidism is something that should be checked, especially when you're having skipped beats, etc. I have hypothryoidism and when my supplement is too high, I will get more arrythmias. Even if they are benign, the anxiety can cause a multitude of problems and limit you in your activities. I get an adrenaline rush from the arrythmia, then tachacardia (fast beats). It can take on a life of it's own. sometimes you can slow it down with brething techniques, or stress reduction exercises. The panic in my case is a byproduct of the "benign" heart condition. I too, am missing being able to exercise for fear of bringing on an attack. I take Atenolol and Xanax and am now on Coumadin. Good luck.