The Ayurvedic perspective
Ayurveda considers that all diseases are mainly caused by our separation from the real Self and from our divine essence. Be it physical or mental, the disease is a consequence of our ignorance of our Inner Self. "According to the ancient Vedic scriptures of India there is a goal to life. We are not simply born, to live, and then to die without some meaning or purpose. Albert Einstein reflected this idea when he said 'God does not play dice with the universe'. Order and reason exist in life. According to Vedic philosophy life is Divine and the goal of life is to realize our inner Divine nature. Áyurvedically speaking the more a person realizes their Divine nature the healthier they are". (the Ayurveda Ecyclopedia")
I would not call depression a disease. I think the term is too harsh and way too rigid. If we consider the disease to be our alienation and our lack of contact with the depth of our being, then yes I would agree to call it that way. Otherwise, I would say that depression is simply a way of getting back to the Self.
Depression is caused by alienation, by the separation from what is authentic in us. It comes when we ignore our most important needs and desires as human beings. Depression comes as a result of the separation from the Self, from our deepest longings. When looked at it closely, depression unveils certain secret desires of exploration. As children, we were not thought to explore, we were not encouraged to go for our dreams. Our society does not recognize love, affection, and even weakness as being important components of our structure. The imbalance and the feeling of worthlessness do not derive from the external circumstances (the loss, the separation, major changes) but from our feeling of shame and discouragement of not being able to cope with it better.
Many times what strikes us the most is our incapacity to cope with a difficult situation. We have the impression that life is only about being strong and apt, ignoring completely our weaknesses, our sensitive points, the areas still in development. In a society which recognizes and praises the best, the strong, the accomplished, we have no choice but feeling inapt, unworthy, hopeless and rejected during times of depression.
Great masters bring up often the concept of ignorance being the cause of all our suffering. When we reflect on this concept and we start to perceive it deeper, not with our intellect but through our own direct experience, we understand that ignorance is that veil that covers our perceptions and makes us look at ourselves in a very limited way. When we go through a deep depressive state for and we take the time to face it, we understand that guilt, fear, feeling hopeless, are just conditioned responses and are not part of who we really are. When we start to read some more about the so called disease, for a while we can feel doomed, without hope, heartlessly put under the category of "depression disease" with the scary future awaiting: antidepressives and the big stamp : PRONE TO DEPRESSION. At this point we have a good chance to abandon, to renounce the possibility of an inner happy life. All of a sudden we lose our sense of Divinity, our connection, we become a CASE, another "victim" of the disease. This perspective can make us feel extremely down and hopeless, and we start to believe that we are doomed to a life in depression, having totally lost the hope for a chance to get over it.