I'm going to be trite (again).

Knowledge is power, and understanding what is happening to us (psychogically—if not physically) and being able to recognize it for what it is can be very empowering.

In this case, depression is a part of two phenomena.
The Kübler-Ross Stages of Grief as applied to chronic illness, and
The Vicious Cycle of Pain, Depression, and sometimes other factors.

In both cases, the depression—if secondary to pain/grief and not primary—can often/usually be overcome, thought it's not easy, and like pain and other symptoms, there can be ups & downs, and recurrence.

http://tinyurl.com/2c642oa

Doc