Knock: I think depression in its "disease form" is the one that's chemically based and has nowt to do with external triggers neccessarily. The "shit happens and turns your life to shit for a bit" form of depression may be superficially similar but tends to be far more short term, will almost always (if not actually always) sort itself out with time, and generally doesn't require lifelong management of some form or another.
Neither is a barrel of laughs for the most part, admittedly... So probably makes shit all difference to the one on the receiving end at the time which "version" (if there truly is a difference betwixt my "versions") they have.