Hi Paul. I would say between hobby and obsession...though obsession can be considered a form of mental illness. The "Fat Man" of "The Maltese Falcon" was obsessed with finding the Black Bird. A few murders were of no consequence in it's pursuit. In amateur radio DXing that rare station can become an obsession when pursued above other matters infinitely more important...and when courteous on-the-air conduct is disregarded in order to achieve that end.73 Dick
Many great things have only been achieved because someone was obsessed. I think it is mental illness to become obsessed about something of no importance. To me it is not important to work a new country, nor to spot a bird for the first time, which is why even though I like to work distant places and see new birds I am neither a DXer nor a twitcher.
It's OK to be a little crazy....it adds to the excitement of life.