What causes a person to die on ecstasy?

Contrary to popular belief, there have been ZERO deaths attributed solely to ecstasy use.

Death can occur when ecstasy is used in combination with other drugs, and if enough is ingested, overdose may occur (research is currently being done on the neurotoxicity of ecstasy, but not conclusive results have been found).

The most common way (though still rare) to die on ecstasy is dehydration, usually occurring at raves or clubs. When a person stays out all night partying and doesn't get enough water, they may dehydrate to the point of death. Inversely, if someone overcompensates and drinks TOO MUCH water, death may also occur. However, considering the fact that if someone takes ecstasy at home sitting on their couch, dehydration won't occur, this seems more of a problem with the rave/clubbing scene than a problem with the substance itself.