Severe sodium deficiency is referred to as hyponatremia in medical terms and is life-threatening if left untreated. In this, the concentration of sodium in the blood drops to an abnormally low level and this affects the individual because sodium is an electrolyte and it regulates the water content of the cells. When there is less sodium and more water in the body, the cells swell up and this triggers several health issues. The common symptoms of sodium deficiency are nausea and vomiting, headache, confusion, energy loss, fatigue, irritability, restlessness, muscle weakness, cramps, seizures and coma. These are initial signs of the disorder and one should visit a doctor immediately after identifying these signs.