'Not too unhappy?' he said, getting to his feet.
'Of course I'm unhappy. But it's quite bearable. Even interesting. I'd like to work it out on my own, for however long that takes...'
Altered States, ch. 15
Depression can be quite fruitful if it leads to thoughtfulness, inwardness. Certainly my parents' deaths, certainly disappointments in love have led to periods, yes, quite long periods of depression - but they haven't been entirely defeating, you see, they've been quite nourishing. Because you're very receptive when you're in that state: in fact, it's invaluable.