@mikeyp, your magnesium deficiency suggests that you might have a kidney problem -- or a dysfunctional hormone generator such as thyroid or adrenal gland. You might consider asking a nephrologist and an endocrinologist for their diagnoses. My problem was resolved in that way; I had potassium deficiency that cardiologists, internists, and another nephrologist decided was "essential" and of unknown cause or importance. My second nephrologist cared about finding both primary and secondary causes and enlisted an endocrinologist in the search. Together, they found an inherited kidney dysfunction (Liddle Syndrome) that let the potassium get away but gave lab results of a fake ("pseudo") hormone condition. My mystery and yours seem familiar, and I hope you find the answer soon.