Another cause of hyperhemoglobinemia is dehydration. Dehydration is the depletion of body fluids and, when severe, can be life threatening. A common cause of dehydration is excessive vomiting. Vomiting may be the result of medication, stress, pregnancy, food poisoning, head injury or viral infection (like stomach flu). Signs of dehydration include unusual thirst, sunken eyes, dry mouth and cracked lips, infrequent urination or dark yellow urine, and skin that is no longer elastic. If the high hemoglobin level is due to dehydration, it will return to normal when the person becomes hydrated again.