Raison, CNNHealth’s mental health expert at the University of Arizona in Tucson, writes, “Severe major depression is probably the most unbearable pain a human being can withstand for any protracted period. Many people who die of cancer have written eloquently about how the crushing pain ... paled in comparison to the pain they felt when depressed. It causes one to see the entire world as pain. It feels painful inside, but it also feels painful outside.”