Folks, I can't explain everything. What I can tell you is that emphasis on levels of potassium only catches some cases, perhaps missing the majority. You are repeating a misunderstanding which turns up in many M.D.s.
The serum ion levels that are easy to measure are a small part of the story. Movement of potassium and sodium ions in and out of cells is highly dynamic. Every time a neuron fires there is movement of potassium, sodium, chloride and calcium ions across membranes. Intracellular concentrations change rapidly.
Calcium is important not just in nerves, but in every situation where biochemicals stored inside vesicles in cells are released when those vesicle fuse with cell membranes. That was why Gingergrrl's doctor tried calcium channel blockers to treat MCAS. He/she was hoping to reduce activity of mast cells. Unfortunately, she had a specific problem with antibodies to N-type calcium channels which this exacerbated.
You also find a great deal of movement of ions into and out of muscle fibers during activity. Sharp distinctions between neurological and metabolic activity only occur in textbooks.
Recently, I've been particularly interested in
metabotropic receptors. These are surprisingly complicated. They respond to neurotransmitters and control ion channels, but this is not a simple mechanical operation. Biochemicals called second messengers are involved, and so are protein kinases. There are a number of ways operation can fail, and so far medicine has only addressed some of these in a few locations.
Typical ionotropic receptors operate on a time scale of milliseconds, but metabotropic receptors can function on much longer time scales of seconds. This is still too short to show up on common clinical measurements, where doctors are looking for readings that are stable for hours or days.
Life is a process of managing continual change. Defects in processes can produce changes in levels, but this is far from universal.
I'd liken current medicine to an automobile mechanic who does nothing until the engine in your car is in danger of seizing because the level of oil in the crankcase is too low. Had he paid attention to the oil drips on the driveway he could have seen the pathological process leading to failure, and followed this back to leaking seals. "Nah! We see that all the time. Lots of cars leak oil, and keep on running."