water intoxication

Don't worry: It's more than you could physically drink.
Symptoms of over-hydration (water intoxication) include staggering/loss of coordination, lethargy, nausea, bloating, vomiting
When the sodium concentration in extracellular fluid drops, the cells start filling with water as the body attempts to balance
The deejays in the case of Jennifer Strange clearly knew they were promoting a dangerous stunt -- they just did not bother to tell the contestants of the danger.