This all happens without the knowledge of the deceased. Depression is akin to the beginning of a mental ice age. Before the victim understands what is happening the warmth of the sun is replaced by the onrushing freeze. He is dying a mental death. His brain begins to slow down like a mountain stream in the dead of a harsh winter.
Thoughts barely trickle between the ice that blocks their free flow.
He desperately seeks the warmth that will melt the glaciers that are carving deep dark crevices in his psyche. The bitter cold settles into the pleasure centers of his brain and pushes out the emotional warmth that once nourished him. As this ice age covers more of the emotional landscape the victim tries everything to free himself and escape the deep dark freeze that keeps pulling him down. Slowly, any and all warmth that once dominated the visionscape of the mind is replaced by the desperation and bitter cold of emotional pain. Unfortunately, depression doesn't kill all of the brain and stop one from breathing.