Which symptom might indicate severe hyponatremia?

Severe hyponatremia can lead to significant neurological symptoms due to the rapid changes in serum sodium levels, which affect the brain's osmotic balance. Lethargy and progression to coma are particularly concerning manifestations of severe hyponatremia. This occurs because low sodium levels can cause brain cells to swell, leading to increased intracranial pressure. Symptoms may escalate quickly, and severe mental status changes such as lethargy, confusion, or even coma signal that the hyponatremia is affecting central nervous system function, requiring urgent medical attention.

While nausea, headache, and dizziness can also occur with hyponatremia, they are generally not exclusive to severe cases and can be seen in less severe sodium imbalances. The presence of lethargy and possible coma highlights the critical nature of the condition, making it a key indicator of severe hyponatremia needing immediate evaluation and treatment.