A low sodium level in a blood test means that the concentration of sodium in the blood is abnormally low, a condition known as hyponatremia. Sodium is an electrolyte that helps regulate the amount of water in and around cells, supports the work of nerves and muscles, and maintains normal blood pressure. A normal blood sodium level is between 135 and 145 milliequivalents per liter (mEq/L), and hyponatremia occurs when the sodium in the blood falls below 135 mEq/L. Causes of low sodium levels in the blood include drinking too much water, losing sodium through sweat, hormonal changes, adrenal gland insufficiency, low levels of thyroid hormone, kidney failure, heart failure, cirrhosis, and use of diuretics. Symptoms of low sodium levels include weakness, fatigue, confusion, headache, nausea or vomiting, muscle weakness, twitching, or cramps, seizures, and coma. The treatment for hyponatremia depends on the underlying cause and severity of the condition and may include restricting fluids, stopping the use of diuretics, medications, and intravenous fluids.