I used to hear people say "how are you doing?" in the meaning of "how do you feel" (and that's why people used to answer "very good" or something like it. As a non native English speaker it's difficult for me to understand it and it always interests me to know what is the relation between "doing" to the meaning of feeling.
Editing: I checked the question that was said to be duplicate, and I didn't find any similarity to my question. I am asking about the relation of the noun "doing" to the meaning of "feel". No relation between them for my opinion.