Depression is different from sadness. Being sad is a biochemical response to a negative stimulus, something that affects you personally. Generally you can feel its superficiality even if it causes you to stagger initially. Its solid in shape, form and transient in nature.
Depression is insidious. It seeps into your skin and settles into your bones where its impossible to grasp or understand because its amorphous; transparent yet dense. Everywhere and nowhere. It is all through you. In you. A paralysis that spreads like fire, coursing through your body along your circulatory system so that every cell is affected. Infected. The worst kind of resistant infection, because death from depression is slow. Painfully, achingly, patiently slow.