Depression - The Black Dog
Depression is often referred to as "The Black Dog". According to Wikipedia, the term "The Black Dog" was first used by the English writer Samuel Johnson. It was then popularised by Sir Winston Churchill who also used the term to describe his own depression. As a result the term "The Black Dog" is in common use today to describe depression.
But what exactly is depression? It can be so different for so many people and sometimes words are not enough to describe the feelings, or lack therof, that are involved. A video might be easier to understand.