What Causes Rapid Heart Rate, Shaking And High BP?

I have problems with potassium. For years I had to take potassium to stay at 2.8. I have attacks of rapid heartbeat, shaking, high blood pressure, sweating when it drops. I also have strange salt cravings. A few months ago suddenly my potassium was up after 6 years to 3.8. Then it went to 4, then to 5. I quit taking potassium and am waiting to have another test now. I have a dad and a grandson with these strange attacks. I was also recently diagnosed with POTS, but these attacks of symptoms coincide with a drop in potassium and dehydration. My kidneys have been cleared. I believe I have a potassium problem at the cell level, but what specialty of doctor even handles this? The Neurologist didnt seem to know anything about potassium problems at the cell level.