What are the early warning signs of ecstasy pills going wrong?

I was just wondering if anyone could give a basic, straight-forward list of symptoms that would indicate that you would need urgent medical attention after taking ecstasy pills?
I probably should have specified that it wasn't about myself I'm asking because I have friends who take pills. I AM NOT THE ONE DOING IT!!
I should also specify that I mean physical signs, not a feeling. Like something that other people would be able to see.

: http://alcoholdrugstreatment.info/what-are-the-early-warning-signs-of-ecstasy-pills-going-wrong