Symptoms The main symptom of hypernatremia is excessive thirst. Other symptoms are lethargy, which is extreme fatigue and lack of energy, and possibly confusion. Advanced cases may also cause muscle twitching or spasms. That’s because sodium is important for how muscles and nerves work. With severe elevations of sodium, seizures and coma may occur. Severe symptoms are rare and usually found only with rapid and large rises of sodium in the blood plasma.