Recurrent Depressive Disorder.
It has a lot of names, probably because nobody really understands it. I have it. I have it bad.
What is it?
Well, it's a theory, really. Or, several competing, sometimes conflicting theories. There's the monoamine hypothesis, the biopsychosocial hypothesis, the evolutionary hypothesis, and so on. I can't tell you which, if any of them, is right. Probably none of them, considering how little we know about the brain (not much) and its relation to thought (nothing whatsoever). Also, I don't care which, if any of them, is right, because to me depression is not a theory, it's life. My life, whatever that means.
I can't tell you what my depression is to a doctor or a scientist. But I can tell you what it is to me. That part is simple. But first, let me tell you what it isn't.