Dave,
As a person who once experienced severe depression after cancer treatment, my advice to you is to get medical help as soon as possible before the situation deteriorates.Whether you like it or not, anti-depressants are essential if your mind is full of negative thoughts: feeling guilty and helpless.For me, not only nights were intolerable but also day time when I was all alone without any enery or drive to do anything. It is good that you can ventilate here but after all,we are not medical professionals. You may need some medical counseling. There is light at the end of the tunnel. Cheer up.

Karen