As a Noun: 1. Hyponatremia occurs when a person has an abnormally low concentration of sodium in the blood. Too little sodium can cause cells to malfunction and extremely low sodium can be fatal. Note: 1. There appears to be no commonly used Auslan sign for HYPONATREMIA. If you know a sign for HYPONATREMIA used by you or other Auslan users (deaf people or interpreters) please go to "report missing sign" and supply details. Thank you.