Why Black Dog?
Winston Churchill famously referred to his experiences of depression as "the Black Dog", and the concept was later used by Matthew Johnstone to create a beautifully illustrated book about living with depression called "I Had A Black Dog", a picture of which is shown above.
This conceptualisation of depression, and more generally mental illness, has always appealed to me. For those suffering from emotional distress, words like "Major Depressive Disorder" or "Generalised Anxiety Disorder" can seem to have little relation to the day-to-day lived experience, and although the idea of a black dog won't fit for everybody either, it does seem to capture something of the experience that clinical definitions overlook.
I also like Johnstone's ideas about dealing with the black dog - that by understanding it, talking about it with others and finding ways of managing it, we can become its master rather than the other way around. Emotional distress might be a part of our experience, but it does not need to control it or overwhelm us.