I can't respond in direct response to your question, but seeing your post go unanswered, I offer the following.
I have seen many posts on tachycardia that to my memory sound a lot like what you are describing.
I assume you have been examined by a doctor and have a medical diagnosis of what you are feeling.
My recollection again is that what you are feeling is not threatening if the HR isn't too high and the duration is short. I don't have firm numbers, but I'd estimate a HR over 200 is a concern even if short term (minutes), and a HR over 130 is a concern if permanent. I'm talking resting HR here.