I was diagnosed with Graves disease (hyperthyroidism) 5 years ago. Lost like 30lbs in 3 weeks. Ate away at my muscles and could barley stand. Doctors really pushed destroying my thyroid by radioactive iodine after 2 years of taking tapizole to slow the thyroid. They destoyed my thyroid and a month later had gained 30 pounds. Never been the same mentally after. Sluggish. Thyroid controls so much you never no until its gone.
After doing more research we now believe I had hypercalcemia. Too much calcium. Not enough Magnesium and potassium. I sweat alot and the time I was diagosed 5 years ago I was big into running, sitting in the sauna 30 minutes a day on top of being already a sweaty guy. We believe I sweated out alot of magnesium which is a muscle relaxer(heart) and too much calcium(mucsle contractor, heart) That could be why my heart was racing.
Anyway I wish I could go back before my thyroid was destroyed and try to limit my calcium intake, stop running, stop being in the sauna and take more oral magnesium and transdermal magnsium oil to get more and see if my heart calmed and muscles relaxed.
Do a google search on hypercalemia, magnesium and the heart.
Good luck.