I have a bookmark I picked up this summer in DC at the Roosevelt memorial that has a quote from Eleanor Roosevelt:
"No one can make you feel inferior without your consent."
I find that to be such an empowering statement.
I also have those really slow days when I don't get enough sleep. I don't even attempt to do something complicated at work when I feel like that. It was really bad when the kids were little and waking up every 2 hours.