Hyponatraemia - Symptoms

What are the symptoms of hyponatraemia?

The symptoms and severity of hyponatraemia depend on the following two factors:

  • The level of the blood sodium.
  • How quickly the sodium level falls - hyponatraemia can be divided into acute or chronic. In acute there is usually a sudden fall in blood sodium levels (over hours), whereas a chronic fall occurs over days to weeks.


The clinical picture can be confusing, as mild hyponatraemia can cause significant symptoms if the drop in sodium level is sudden, whereas severe chronic hyponatraemia can cause no symptoms, due to the body (especially the brain) adapting to the lower levels. Symptoms include:

  • Mild hyponatraemia - lack or loss of appetite (anorexia), headache, feeling sick (nausea), being sick (vomiting), and lack of energy and enthusiasm (lethargy).
  • Moderate hyponatraemia - personality change, muscle cramps and weakness, confusion, and lack of muscle co-ordination (ataxia).
  • Severe - drowsiness and fits (seizures).


A healthcare professional may pick up on the following features:

  • Neurological signs:
    • Reduced level of consciousness.
    • Problems with cognition such as, short-term memory loss, disorientation, confusion, depression).
    • Seizures.
    • In severe acute hyponatraemia the brain stem can press down on the bottom of the skull (called herniation), leading to a large pupil that does not respond to light, coma and the patient stopping breathing.
  • Signs of low body fluid (hypovolaemia):
    • Dry mucous membranes - for example, the tongue and the mouth.
    • Sunken eyes.
    • Fast heart rate.
    • Low blood pressure.
    • Dry skin or reduced elasticity of the skin.
  • Signs of an increase in body fluid (hypervolaemia):
    • Crackles when listening over the lungs.
    • Extra heart sounds as the heart is having to work harder.
    • Increased pressure in the veins seen at the neck.
    • Swelling of the tummy (abdomen).
    • Swelling of the legs.
  • There may also be features of the underlying cause, such as an enlarged thyroid gland in the neck with thyroid disorders.

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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.