I am not sure I am sold on the transdermal spraying of magnesium versus oral intake. I sprayed heavily in some areas and got a rash, perhaps that was the chloride part of the magnesium chloride.
Magnesium can have interactions with other minerals and I am thinking that perhaps some of the issue may have to do with the potassium/sodium balance. These are also cations (along with magnesium) while chloride is an anion. Simply putting they are electrolytes.
Maybe you describe your health problems if any, normal diet and any other supplements. Usually the dry mouth is indicative of electrolyte problems, testing thru a lab like Exatest or Traceelements.com can be a big help in which they can pick up imbalances of minerals, I prefer the latter.