Adam Kirsch in Tablet:
The problem with depression—the thing that makes it so hard to describe, and gives its sufferers a bad conscience—is its resemblance to unhappiness. Unhappiness is part of every life, and most people learn how to cope with it: by changing the conditions that cause it, or by distracting themselves, or by actively repressing it. A person who can’t deal with being unhappy is seen as a moral failure—childish, selfish, “difficult.” It is all too easy to apply the same judgment to a depressed person, as if depression just meant luxuriating in unhappiness. David Foster Wallace wrote a brilliant story, “The Depressed Person,” in which a woman worries that by describing her suffering she will only disgust her friends and even her therapist—a worry which itself feeds into her suffering. But depression is actually the opposite of unhappiness, because it is precisely not “a part of life.” When you are unhappy, life is pressing you, hurting you, and you are forced to respond to it. An unhappy life is a problem, and to be absorbed in a problem is to be absorbed in existence. When you are depressed, on the other hand, there is no problem, because there is nothing to be solved. Existence itself seems to retreat, to leave you stranded, without purchase on things, people, yourself. In her new memoir, This Close to Happy: A Reckoning with Depression, Daphne Merkin describes it this way:
Now you can no longer figure out what it is that moves other people to bustle about out there in the world, doing errands, rushing to appointments, picking up a child from school. You have lost the thread that pulled the circumstances of your life together. Nothing adds up and all you can think about is the raw nerve of pain that your mind has become—and, once again, how merciful it would be to yourself and others to extinguish this pain.
This is the situation that Heidegger called anxiety, and that Sylvia Plath describes as being covered with a bell jar.