All I can say is that it's just too bad that you have to feel like you do. Our society is sooo goal oriented and if you're not producing then you have no use. Not all societies are like ours. Some honor people who are outside the "norm". Also remember that you have a disease as devastating as cancer. If you've tried every avenue available then it isn't your fault. It's the way your body functions. Since you are in bed in a quiet environment maybe as an experiment you could try visualizing something. Create a world in which you could live. If you believe in god then you could spend that time praying. Not necessarily for something but just kind of talking to it. Make god like a friend who will listen to you without judgement. Make the world you create as wonderful as you want it to be. After you do that you may want to write it in a journal and maybe illustrate it.
Anyway, you have us and we won't judge.