I so get what your saying...
I'm trying to do my PhD but it has been complicated greatly by my BP diagnosis... losing you PhD is almost like losing a person, you have to grieve...
We put so much pressure on ourselves and the fear of not succeeding is so huge that it really stuffs you around...
I've found that dealing with some of these issues with a good counsellor/psychologist when you are feeling ok means that you have better ways to deal with the bad thoughts when you are depressed and more susceptible...
By the way, I don't think your a bad person, just a person person, with good things and not so good things, just like every other person. When you are depressed the you see only the not so good, when you are manic you see only the good...
Hope you feel better soon...