Anxiety and "the fear of the fear" causes the heart rate to increase dramatically. Given just the facts of your youth, your female sex, your normal weight and good blood pressure, your chance of occult heart disease is approaching zilch.
When you factor in your your severe anxiety--most notably being bedridden for months due to this problem--Inwould say your chief problem, the one currently preventing you from enjoying your life--is untreated panic/anxiety plus a cardiac neurosis (you can google it).
I believe you need to get a good psychiatrist and discuss--and receive treatment for--chronic, severe anxiety.
Breathe.... Yes stop and take a deep breath. You'll be surprised how just doing that can bring down your anxiety level.
However please note that your HR going up when you are active is Perfectly Normal. Same with your BP. When we are active our heart pumps more oxygenated blood to various parts of the body. That brings up the HR. Docs told me that to have an accurate reading of BP and HR you should be sitting and have been "at rest" for at least 15 minutes. Other than those times you are going to get varied readings and an elevated HR.
Sure hope this helps.
This is not anxiety. Go see a cardiologist and get tested for POTS syndrome. Also, make sure you don’t have an adrenal tumor (called pheochromocytoma)
You mentioned wearing a hear monitor, under prescription? Cardiologist? The anxiety is in need of management, no other advice from me, sorry. A beta blocker, maybe at a very low dose may help and that can be prescribed by a primary care or cardiologist. I have taken beta blocker meds for almost 20 years and find it effective in lowering my heart beat now driven by atrial fibrillation, that is I suffer form heart disease, maybe you don't, but I offer discussing using a heart rate lower med such as beta blocker with your doctor. Good luck, we all need that in the anxiety driven world we find ourselves in beginning in 2020.