You have to be a gate-keeper of the negative destructive thinking. (easier said than done, I know) and you have to come up with a bunch of positive things to argue with that little bastard in your head when it comes up.

Write them down. The good statements you'll say back when that voice says;
you're not good enough, you're worthless, you can't do it alone, you're fat, you're damaged... etc.

Fight it. That's what I learned and did when I was well. And that's what I'm going to start doing again.