Your doctor will take appropriate precautions to minimise the risk of this. • Low blood levels of some substances: — low calcium levels, which may cause muscle cramps, abdominal cramps or spasms — low magnesium levels, which may cause muscle weakness, confusion, "jerky" movements, high blood pressure, irregular heart rhythms and decreased reflexes with severely low blood magnesium levels. — low potassium levels may cause a feeling of weakness — low glucose levels, which may cause nausea, sweating, weakness, faintness, confusion or hallucinations.