My first thought when reading your posts is a concern for the stroke. If all the testing (and I'll assume CT and/or MRI of the brain) was negative, then the 'stroke' was likely a TIA, or mini-stroke. Your symptoms suggest this as a possibility. Now, what would be causing a stroke at your age...that's the question. Have they checked aCL (anticardiolipin) for antiphospholipid syndrome? If not, I would ask for the simple blood test to confirm or rule this out.

Also, have you been checked for autoimmune diseases...ANA, RF, SSA, SSB, etc? Has anyone even considered an autoimmune angle on your problems?

Could you tell me if you have other symptoms...even if they seem insignificant? Anything like dry eyes, mouth, unusual fatigue, joint pain, rashes, unusual nausea or fullness even after eating just a little, fullness that lasts a long time. Anything might be important.

As for the heart rate/rhythm, sound like you may have some autonomic dysfunction. Do you have problems with your BP dropping when you stand? What about balance? What meds are they using to control your tachy rates?

I know it's a lot of questions, but the more info your provide, the easier it may be to offer suggestions.