I have a Black Dog of my own, and I can say that there is no particular or specific reason for it to suddenly seize you.

I lost an entire day. People at work were saying they had told me things, that I had agreed to do things, and I could not remember having done so. I mean, I'd phased off before, for a few minutes, an hour. But to go through a whole day, apparently reacting and behaving normally, but to apparently not have actually been there....Scary! That night I dreamed that a little girl with a skull for a face was showing me a box of limbless, eyeless kittens. I saw the doctor the next day; he put me through the questionnaire and on medication before giving me a four-week sicknote.

That was four years ago. I've had CBT, Counselling and more medication. The Black Dog still follows me around, but I've learned to keep him at a distance. When I do have bad days,. I meet them in the Stoic manner, as being one of the things that is not within my power, and do my best not to let them affect how I behave and think.

There is never just one reason for it, humans are too scatterbrained and resilient for that!