Here's a page about the ways E can kill you:
http://www.thesite.org/drinkanddrugs/drugsafety/drugsandyourbody/canecstasykill?view=print
Bear in mind that in Britain about 4m people have taken ecstacy, and there have been only a few hundred deaths. Your character is about to get very, very unlucky.
As to effects: firstly, E doesn't make you hallucinate. A, um, a...friend tells me this is what it feels like.
Firstly you swallow the pill (or commonly half a pill) with your drink. You're doing something illicit with other people, so there's a sense of cameraderie and shared risk. Basically nothing happens for a bit as you wait for the drug to enter your system.
After a while, you start "coming up". This feels like somebody just dumped a load of adrenaline into your body: your pulse speeds up, you start taking deep breaths, you talk a bit more loudly and confidently and you're basically a little more extroverted.
For my friend, the main effect of the drug was making him feel this kind of upswelling of love for everone around him. He was with some casual friends and for that night he just felt that he loved them all so much, and he just wanted to help them and hang on their every word adoringly. He also tells me he got extremely horny, and went on to have really amazing, experimentative sex with one of the girls. (Just reporting the facts.) Imagine two people in a shared conspiracy feeling they totally love each other, and also that they're really confident and they can communicate absolutely freely, and you reach the equation E = great sex. :-D
The come down occurs a couple of days later. Basically you feel listless and depressed, and easily upset. That goes away the next day.
As you come to use the drug more, you learn to recognise and manage the highs and lows. You still feel the love and the depression, but you recognise that it's not really you but the drug, and you learn to disassociate yourself from the feelings.
So those are the normal effects. I'd
imagine that if you started dying of heatstroke during the "up" phase, you'd hit the comedown immediately, and swing from great elation to great misery. Symptomatically you'd be dying of heatstroke or liver failure or whatever. I guess you'd feel the same as anybody else dying of liver failure, just more depressed and emotional.