Darkness Visible: A Memoir of Madness

by William Styron

a veritable howling tempest in the brain, which is indeed what a clinical depression resembles like nothing else

But never let it be doubted that depression, in its extreme form, is madness. The madness results from an aberrant biochemical process. It has been established with reasonable certainty (after strong resistance from many psychiatrists, and not all that long ago) that such madness is chemically induced amid the neurotransmitters of the brain, probably as the result of systemic stress, which for unknown reasons causes a depletion of the chemicals norepinephrine and serotonin, and the increase of a hormone, cortisol.