The following description of depression at WebMD is common:
When you have depression, it’s more than feeling sad. Intense feelings of sadness and other symptoms, like losing interest in things you enjoy, may last for a while. Depression is a medical illness, not a sign of weakness…
There is another side to some people’s depression. Suppose we think of depression as caused by a lack of something or things that make normal life mentally possible. For example, perhaps you are facing a boring day of meetings with people all too prone to complain and delay; still, you can get out of bed, have a reasonable breakfast, arrive at work well-groomed, and so on. When depression of the sort described above hits, all that becomes much more difficult, and maybe sometimes so close to impossible that you don’t do it.
It is important to know that for some people there is quite a bit more to depression. Something fills in the lack, and it is pretty horrible. Kay Jamison writes about this in today’s NY Times:
Suicidal depression involves a kind of pain and hopelessness that is impossible to describe — and I have tried. I teach in psychiatry and have written about my bipolar illness, but words struggle to do justice to it. How can you say what it feels like to go from being someone who loves life to wishing only to die?
Suicidal depression is a state of cold, agitated horror and relentless despair. The things that you most love in life leach away. Everything is an effort, all day and throughout the night. There is no hope, no point, no nothing.
Jamison emphasizes that depression even of this sort can be treated. But some people are treatment resistant, and for others the effects of the treatment may be too costly. Facing that relentless horror may drive one to drink or drugs. One may find it completely intolerable, and when faced with it again and again finally decide life is very literally not worth living.
There is a great deal we do not know about depression and suicide. Still more, much about Robin Williams is out of our ken. But it may help to know that most of us can’t imagine what he may have been going through, and those that do go through it may find it impossible to explain, as Jamison says it is for her.
Addition:
I’ve worried over the last day or so that I’ve put something up for discussion that in effect I’ve maintained only the (very unfortunate) cognoscenti know about. One result might be to denigrate the more ordinary thorough misery of a deep digression that does not involve this mysterious horror. That would be very unfortunate. Or it might just leave people not believing in that horror as a phenomenon. I think that would be a shame since I expect it is a clue for why some people find suicide is a reasonable option. So I looked up “the horror of depression” and found that sometimes when it occurs the depression is called psychotic depression. William Styron’s description of his depression might help one see the label as appropriate:
For as Styron discovered, true depression swallows its victims entirely, devours them in one huge gulp, then spirits them to an otherwise unknowable nadir.
“To most of those who have experienced it,” Styron writes in “Darkness Visible: A Memoir of Madness,” a slim volume Random House is publishing this month, “the horror of depression is so overwhelming as to be quite beyond expression.”
But if there were a single designation for this disorder, a word or a phrase, Styron believes it would be something like brainstorm , meaning not some burst of intellectual inspiration, but “a veritable howling tempest in the brain.”
That is how it felt to William Styron, the Pulitzer Prize-winning author of “Lie Down in Darkness,” “The Confessions of Nat Turner,” “Sophie’s Choice” and other books and plays. At his year-round home in Roxbury, Conn., five years ago, Styron’s family watched helplessly while he moaned and shouted from his bed.
“My head is exploding!” Styron cried. “My head is exploding!”
The next day, he entered the psychiatric unit of Yale-New Haven Hospital for the treatment he believes saved his life.
Feminist Philosophers 