It is not in common use in the United States, and the Language Arts teacher who jumps up and down and turns an unpleasant shade of lavender because you said you are "well" today and one never uses an adverb with a "linking" verb like "to be" will fall over frothing if you say "poorly" when asked about how you feel.
The word "poorly" is almost never used in the U.S., and when it is, it's only used as an adverb. (Oxford lists it as an adjective only in British English.) The opposite of "I feel well" is "I feel badly" when speaking of health. When speaking of general states, I would say, "I feel good" (or I'm doing well) and "I feel bad" (or I'm doing badly). I suggest adding "badly" and possibly "bad" to the acceptable responses.
not only according to what i have learned but according to my latin teacher, this is a very loose translation. there are many ways to translate habeo, but to feel is not one of them. this would rather be 'i hold myself poorly'. this could maybe be sentio malo? or sum malo.