What kind of magnesium are you taking and is it the same kind and brand you've always taken? Are you taking any calcium or have you changed your diet recently so that you're eating more calcium foods? Just wondering about the calcium/magnesium ratio here.

Also, you can buy potassium chloride powder: http://www.iherb.com/Now-Foods-Pota...-8-oz-227-g/777

Some salt substitutes are also available from grocery stores that are potassium chloride, such as "No Salt" or "Nu-Salt". They're not pure, though.