Causes. Sodium plays a key role in your body. It helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body's fluid balance. A normal sodium level is between 135 and 145 milliequivalents per liter (mEq/L) of sodium.Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L. Many possible conditions and lifestyle factors can lead to hyponatremia, including: 1  Certain medications.t helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body's fluid balance. A normal sodium level is between 135 and 145 milliequivalents per liter (mEq/L) of sodium.