Severe magnesium deficiency is extremely rare. The first sign of a deficiency is a serum magnesium level below normal – called hypomagnesemia (magnesium deficiency). Over time, the serum calcium level also begins to drop, even though PTH (parathyroid hormone) rises to compensate for the loss and even though sufficient calcium is ingested with food. Normally, PTH causes calcium to be mobilized from the bones to increase serum calcium levels to counteract hypocalcemia. As magnesium deficiency progresses, PTH also decreases, along with serum levels of potassium whereby sodium is retained in the body. Signs of severe magnesium deficiency include hypomagnesemia (magnesium deficiency), hypocalcemia (calcium deficiency), hypokalemia (potassium deficiency), and low serum PTH concentrations. In addition, probably due to hypocalcemia, muscle cramps and tremors, loss of appetite, nausea, vomiting, and personality changes occur.