I don't have enough information on when to see a doctor.

Could be anxiety, could be an electrical disorder of the heart. Could be haywire endocrine system leading to excessive adrenaline secretion. Also under endocrine problems, hyperthyroidism. I would assume these have all been ruled out if all you have left is nitro...? Or is the apparent tachycardia (heartbeat persistently or occasionally above 100 BPM when under no exertion) new and after the determination that nitro should help you?

Either way, you should not seek practical and discovery medical help on these fora. You really ought to consult a physician who knows your case.

You should see your regular doctor for a full set of labs and tests.
Good luck.

The symptoms you describe are very familiar to me, I have recently been diagnosed with CHF. I too have the same questions and am wondering if anyone knows if there is a CHF Support group on this site. This disease has many ramifications and it would be helpful to know what to expect and how to deal with it.

Send a message to your doctor and ask them or call them.
That is what I was told.

Sounds serious. Please have a doctor do appropriate tests and make a professional decision for you. You can’t possibly provide us with enough information to advise you. We are no substitute for a doctor except we can all tell you to go to one. Only with appropriate labs and test and a doctor asking all the pertinent questions will you get the answer you’re looking for. Good luck.