IN MY OPINION the cause of depression is negative emotional retention.
It is a proven fact that the sub-concious mind retains negative emotions every time you are not able to process them properly. My personal experience with severe depression and anxiety showed that I had simply retained depressive, anxious emotions. I went through a tramatic, depressing experience where I could not process the emotions properly.
All day, every day I felt the same emotions that were experienced a year before in those events. When I went to the doctor, he did now know how the problem was caused or how it would be cured, but offered anti-depressants. When I went to the counselor, she did not know how it was caused and how it would be cured, but offered advice. When I went to the NERT specialist, he knew what caused my problem and how it was to be cured. He released the depressive, anxious emotions from my sub-concious mind. I went from a clinically depressed to an absoluetly happy man. When I went back to the doctor and counselor, they were lost for words and took into consideration that I had been 100% cured. They also considered practicing negative emotional release treatment at the medical centre.