If you review some of the other posts in this forum, and some of the blogs, you will find that depression after completion of treatment is very common. I have battled it off and on for the past 15 moths. It was worse the first few months, then improved. I can fall back into a funk more easily now than before treatment, and find that my temper is a bit shorter now than before, especially if I am a little short on sleep, which has been happening a lot recently with job craziness.
There is a considerable body of literature out there that talks about cancer patients suffering from a form of PTSD, and I do not doubt that a bit. No shame, and lots of benefit, to getting it assessed and treated if it continues to be an issue. I find that eating better, getting exercise, and getting rest really helps. Now if I could only do all those things regularly . . .