Over 100 people have died after taking ecstasy at rave parties. When you take ecstasy in a hot place and start dancing energetically, your temperature rises even more again. With body temperatures raised to these very high levels there is a risk of developing heat stroke. When your body overheats you lose fluid.
Some ravers lose pints and pints of fluid when dancing on E in hot places.
At a crowded indoor rave you could lose up to 6 pints in 6 hours. These fluids must be replaced. These cases are not ecstasy overdoses. Heatstroke can happen even if you have only taken one tablet. Sip water slowly rather than drinking a lot all at once, as this can be dangerous.