I can certainly relate to the OP being that I have had my downs as well, I never saw anyone for it, but do believe that I have gone through a depression as well and can list a variety of reasons for.
Biking has greatly helped, not so much for the actual ride, but because it gets me out of a confinement of sorts and helps me to feel free. Driving a car does not help, or sitting in a cubicle or a small room at home. Doing things like walking a long ways away, jogging, swimming and biking seems to help people whom are depressed to get things off their mind and to relax.
Mine is riding on a trail where I can stop and watch some wildlife, hear a rooster crowing, watch a fox, and even a Coyote (yikes) run by. But I absolutely love being outside and out of a box.