What are the risks of trying ecstasy?

I have never done it before. I have smoked pot, done shrooms, and taken narcotics before. I'm not a frequent drug user, all though I do smoke about every weekend. So this being the first time, I'm not sure what to expect, besides the things I have heard. I only plan on taking a single tablet. I should be fine, right? What are the risks? And how should I expect to feel? This will probably just be a one time thing, like shrooms. Thanks, guys!