What is it?

Hyponatraemia is a low level of sodium in the blood. Sodium levels in the blood have to be tightly controlled. Various chemical messengers (hormones) and organs are involved in this process. For example, hormones involved include antidiuretic hormone and cortisol, and organs involved include the brain and kidneys. There is a very close relationship between body sodium and body fluid levels.

Hyponatraemia can be classified in various ways such as:

  • Timing of the fall in blood sodium into acute (usually hours) or chronic (days to weeks).
  • Level of body fluid as either low body fluid (hypovolaemia), excess body fluid (hypervolaemia) or no change in body fluid (euvolaemia).

What does it feel like?

If the levels are only mildly abnormal you may feel completely fine, or only have mild symptoms such as, feeling sick (nausea) and dizziness. Once the blood sodium levels fall further you may start to have trouble knowing where you are, have muscle weakness, lose your appetite and have sickness (vomiting). As the blood sodium falls further or if there is a rapid fall in blood sodium, you may develop confusion, difficulty getting around and fits (seizures). A coma can also occur.

You may also have symptoms relating to the underlying cause and from loss of body fluid or excess body fluid. For example, loss of body fluid may make you thirsty and you may pass less urine. Too much body fluid on the other hand, may cause you to develop leg and tummy (abdominal) swelling.

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Dr Gurvinder Rull
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
29395 (v1)
Last Checked:
22 May 2017
Next Review:
26 June 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.