There is nothing wrong with you. Your feelings of bewilderment and depression are really quite normal and happen to a lot of us during and after treatment. The depression is chemical and can be caused by the surgery or some of the meds you have been given as they can affect5 the serotonin levels in the brain. The good news is that it is treatable with meds. You may have to see your Primary care Dr. as cancer Drs. are often not very well trained to see and treat this. Please be sure to mention it to them in the next visit.
As for the bewilderment, you have just been through a major and fairly fast change in your life. I suspect that you never though much about cancer before your diagnosis but were faced with this life changing event and then major surgery to take care of it. You are now wondering just what happened? How did you manage to get cancer? Do I need to worry about it coming back? There are probably 1000 questions running through your head at this point. That is all normal and being here at WhatNext is a good place to start getting some answers. You also need to recognize that there are some questions no one can answer. No one knows why me? and it rarely pays to get into questions about what you could have done differently to avoid cancer or things like that as we don't yet have time travel. Ask questions here and of your Drs. You have a right to understand what happened to you and how things will progress in the future. Good Luck and let us know how else we can help.