They're not totally opposite. They share in common "directiveness" or task-focus (as opposed to people-focus, which would explain why you would be drained in social situations just as much as a pure Melancholy. You might express yourself a lot to people, but not respond as much to them (In the system I like the most, we call it "responding as an introvert")
I guess it's the whole "pessimist vs optimist" dichotomy that makes them look opposite; but the Choleric is described as optimistic because of the expressiveness. That's only one dimension in which they are opposite.
Thanks again. Now I can see it better.
I´m reading your "temperament for dummies" link. It was hard to find the test mentioned at the beginning of the site.
"An intelligent hell would be better than a stupid paradise."