I went to a counselor and told her the same things that you are saying (I have two seventh grade daughters and suddenly I couldn't even fix dinner for them or get out of bed to ask about their school day or sit on the porch to watch Evan ride her pony). The counselor smiled, touched my elbow, and said, "if you weren't depressed, we'd be concerned." It helped a little to think, "this is part of it, just like the nausea or neuropathy."
Another time I met with her and she explained to me that cancer survivors--after the scars and torture of chemo and radiation--suffer post traumatic stress disorder. Again, this helped put my feelings in perspective.
I did schedule my treatments on Mondays so that the weekends would be my best days (that's not saying much, but I spent all of the first four days in bed).