I found a great quote that explains the difference between depression and grief, I think, by Patton Oswalt.
As serious fans of his comedy know, Mr. Oswalt has suffered from depression, but this, he said, was far worse. “Depression is more seductive,” he said. “Its tool is: ‘Wouldn’t it be way more comfortable to stay inside and not deal with people?’ Grief is an attack on life. It’s not a seducer. It’s an ambush or worse. It stands right out there and says: ‘The minute you try something, I’m waiting for you.’”
Image info: The comedian Patton Oswalt at the Chateau Marmont in West Hollywood, Calif. Mr. Oswalt’s wife died in April, and it has been a long, hard climb for him to return to comedy. KENDRICK BRINSON FOR THE NEW YORK TIMES