I do not have the juice to google this right now, so please be kind if the answer is obvious:

what is the men's equivalent to hysteria? by which I mean: how was undiagnosable chronic illness explained in men?

And I understand that this is a difficult and loaded question, but it is absolutely not true that all men have always been taken seriously by doctors. (Just like it's not true that all men are taken seriously by doctors now.)

Medical bias is so much more complicated than that.