Okay, I can't find it, but I read this fantastic article about joy on Good Friday. In the last few months, at some of the more difficult moments of depression, some that I had talked to were trying to help me "choose happiness". I can no more choose happiness at that point than I can choose flying. Happiness is a feeling, and while depression may be magnifying things, at that moment, being alone and the emptiness in life that results from that were beyond where I could make any choice for happy feelings.
In my heart, I always make a distinction, that instead I choose joy. My problem was that I couldn't articulate the reason that I felt they were different. I've tried to explain it here before, but not sure that I've really gotten it. The dictionary basically defines "joy" as "happiness", so why would one be okay and the other not? I can only give you what is my own subjective take on it, and the article was what helped me to be able to give words to this thought.
To me, joy is an attitude. It is not denying the pain, or fear, or grief that is present in your life at that moment. Like Mary at the foot of the Cross, this is not okay and it is okay to mourn, to weep, to feel the pain that is inherent when something in your life is broken and objectively not the way that things should be. However, the author of the article pointed out that Mary did so with hope, knowing that this was not the end. That, to me, is joy. In the midst of brokenness, acknowledging that this moment has meaning and value. Of knowing that there is hope for a better tomorrow, in this world or the next. Of holding on to the knowledge that this, too, has an end, and that because of Christ there is new life waiting on the other side of whatever our suffering is. I would add, beyond choosing hope, it is also choosing gratitude. To be thankful, on some level, for what is good in the midst of suffering, though it does not make the pain go away.
And of course, when the new day dawns, and Christ is risen and our suffering is a memory, then we also embrace the happiness that comes along with that.