"a form of torment so alien to everyday experience"

Few people have ever conveyed so eloquently and accurately the indescribable experience of mental illness (specifically depression) as William Styron in his book Darkness Visible.  I am currently re-reading it and wanted to share a few bits from the first couple chapters...

I was feeling in my mind a sensation close to, but indescribably different from, actual pain.  This leads me to touch again on the elusive nature of such distress.  That the word "indescribable" should present itself is not fortuitous, since it has to be emphasized that if the pain were readily describable most of the countless sufferers from this ancient affliction would have been able to confidently depict for their friends and loved ones (even their physicians) some of the actual dimensions of their torment, and perhaps elicit a comprehension that has been generally lacking; such incomprehension has usually been due not to a failure of sympathy but to the basic inability of healthy people to imagine a form of torment so alien to everyday experience.  For myself, the pain is most closely connected to drowning or suffocation- but even these images are off the mark.  William James, who battled depression for many years, gave up the search for an adequate portrayal, implying its near-impossibility when he wrote in The Varieties of Religious Experience: "It is a positive and active anguish, a sort of physical neuralgia wholly unknown to normal life."   (16-17) 

It had become clear that I would never be granted even a few minutes' relief from my full-time exhaustion.   (18) 

Romain told me that Jean was being treated for the disorder that afflicted him, and mentioned something about antidepressant medications, but none of this registered very strongly, and also meant little.  This memory of my relative indifference is important because such indifference demonstrates powerfully the outsider's inability to grasp the essence of the illness.  Camus's depression and now Romain Gary's- and certainly Jean's- were abstract ailments to me, in spite of my sympathy, and I hadn't an inkling of its true contours or the nature of the pain so many victims experience as the mind continues is its insidious meltdown.   (25-26) 

... I would never see Paris again.  This certitude astonished me and filled me with a new fright, for while thoughts of death had long been common during my siege, blowing through my mind like icy gusts of wind, they were the formless shapes of doom that I suppose are dreamed of by people in the grip of any severe affliction.  The difference now was in the sure understanding that tomorrow, when the pain descended once more, or the tomorrow after that- certainly on some not-too-distant tomorrow- I would be forced to judge that life was not worth living and thereby answer, for myself at least, the fundamental question of philosophy.   (28)

**Don't worry, this isn't me trying to hint at some suicidal plan.  Styron did not end up dying by suicide.  And by God's grace, neither will I.