Hyponatremia (water intoxication) is a condition where the level of sodium (and other electrolytes) in the blood gets diluted with too much water.
The normal concentration of sodium in the blood is between 135 and 145 millimoles per liter.
Some common symptoms of water intoxication are headache, nausea, vomiting, muscle spasms, frequent urination, hallucinations, fatigue, mental disorientation and seizures. Symptoms can be detectable when the sodium concentration in blood reaches 120 millimoles per liter, but are usually associated with 110 millimoles per liter.
Severe water intoxication can be deadly and can occur when the concentration of sodium falls below 105 millimoles per liter. (1)