Acute hyponatremia become symptomatic at:

Hyponatremia is commonly defined as a serum sodium <135 mmol/L (<135 mEq/L). In patient with hyponatremia that develops over hours, life-threatening seizures and cerebral edema may occur at values as high as 125 mmol/L. In contrast some patients with more chronic hyponatremia that has slowly developed over months to years may be asymptomatic even with serum levels <110 mmol