How does depression happen? ...Our sense_of_self daily keeps writing in our minds the current chapter of our ongoing autobiography. Whether it is a happy chapter or a sad chapter depends not so much on our personal current events, but rather our skills as a writer. Since most of us were not born with a talent for writing, for telling good happy stories, often we write sad chapters in our ongoing autobiography.
But, so what? Normally I understand that all this is just a story I am continually writing for my own amusement, a figment of my own imagination. It is obviously not real, so I cannot get upset about it. This stuff about "who I really am". But sometimes I am in a state of very low energy, because of sickness, injury, disappointments, etc. In this low energy state of mind, not being able to think clearly, I sometimes start believing that this stuff I am telling myself about who I really am, is somehow REAL.
Not being able to think clearly, I forget that I have made all this stuff up; that there is no real physical object I can point to and say here it is, it is not just only in my mind. And so I get Depressed, thinking that my story is true, that truly I am a bad person, an unsuccessful person, an unlovable person. And I keep remembering moments of my past life that can be used as evidence to rationalize this absurd and supremely overgeneralized conclusion.
And then a friend points out to me that a map of a mountain is not the mountain itself, even a very accurate map; let alone an imaginary map of an imaginary place. And even the best happiest biographies are not the person the biography is written about; let alone an imaginary biography of an imaginary person inside my own head.
So I wake up. And realize that my own thinking has made me sad. By imagining my own stories to be real.