Well... I don't know. I'm 69 & I have something akin to this. (I haven't seen a doctor about it. So I don't have a formal diagnosis for it.) But it sort-of feels like I have a chipmunk rustling around in my chest! It's some sort of arrhythmia I would guess.

In my particular case, I've lived with an ocean liner's load of stress all of my life. And I presume that is the reason I have developed the problem I have. (I suppose it could also be genetic.) Actually I'm kind-of surprised I haven't had a heart attack before this. But, like you, I'm not over weight. I've never smoked. And I don't drink at all either anymore... haven't for quite a few years now. I also get a bit of daily exercise.

So I guess I can't really offer anything with regard to what might be causing your Tachycardia. But I can relate to what you're experiencing. My best wishes to you...