what helps me the most when I'm feeling overwhelmed or down is to rember that I am not just a walking mass of cancer cells...I am a person who happned to have some cells in my body mutate for whatever reason and I'm doing what I can and have to to stop that. But beyond that issue I am still who I was before it happened, I still have a whole life outside of this issue, and the world is still an amazing a beautiful place. Then I focus my thoughts on something that is particularly amazing and beautiful...like my girlfriend and how much she loves me, or the puppies playing outside...or some music that I like that moves me, whatever it atkes or is available at the time. Doing this helps me lift the depression when it gets to me.
...its Ok to feel down and bummed sometimes, but when it gets to the point where you can't snap out of it and you are not functioning and not enjoying life then you realy need to talk to a professional. its a normal and expected part of any large life issue such as your are experiencing...
all my best
david