generally I would not consider myself depressed in a clinical matter, and I think that I am fairly healthy, both physically and mentally. I walk often and fairly frequently do a moderate level of exercise and I think that a link here can be made. However something strange happens when I push myself too far while exercising (most commonly in running or bicycling, but really in any form of exercise where I substantially push myself too far beyond my comfort zone) I become very depressed for no apparent reason. Any ideas or conclusions from this?