A resounding body of research has shown how closely depression is related to relationships in a cyclical fashion: Depression affects the quality of your relationships, and the features of your relationship can affect your level of depression.
Your experience with darkness has shown all those who love and care about you. Not only has it brought us closer together as a family, but the exercises have made us all realize what is important to us in our lives, and where our priorities lie. Even in your dark times, you still change lives.
It is particularly important to identify depression without sadness (anhedonia) because recent research indicates that it may be anhedonia rather than sadness that correlates with poor physical health.
There was never a moment when I said to myself, "Self, it's been two months since you haven't been your cheery self, and if the Zoloft ad on TV is any indication of what depression feels like, you are certainly a sad egg who can't -- or doesn't want to -- catch that damn butterfly."
We should continue our cultural tradition of recognizing grief as a normal (and expected) human experience. If anything, the grieving person may benefit from support and sympathy, rather than being diagnosed as mentally ill and treated as such.