Cramps, Charlie Horse'es, and the like. I know these. It when you get those rolling cramps that wont let up and remain sore for days after. They are scary. Certainly they are related to Calcium, Magnesium, Potassium, and Sodium. But which one and what combination. You never know which one you need a the time. And even if you drew blood and checked your levels two hours latter they would be different.

I think the worst cramps are simply a disorder of the cellular transport of electrolytes though your body at the time. As for severe cramps its usually Calcium transport in and out of the cells. Note that transport is not necessarily deficiency.

Look up "Tetany". Its a bugger and describes many of our severe cramp symptoms.
https://en.wikipedia.org/wiki/Tetany