Are you dumb, or are you just anxious and sheltered? Your sentence about grad school makes me think it's the latter. There are a lot of people like you in the world of academia.

Read some studies about intelligence in Africa and they found that the kids who weren't smart enough to do all the complex practical work (like tying and repairing nets) were the ones that parents sent to school, where at least they'd be out of the way.

Maybe that's what happened to you?

First change your mind, becomes optimistic to maximize your resources, opportunities and mind.

Diet, lifestyle, sleep, social can all have huge impacts on your mind.

Start with good uninterrupted sleep, no sugar, no alcohol.. see if you notice improvements, keep a daily mood journal for tracking

You're not giving us a whole lot to work with here. What specific behaviors do you exhibit that you don't like and what kind of challenges are giving you problems in particular?

You say that looking for a job sounded insurmountable. What part of the process seemed most daunting to you and why?

Don't tie your self worth to a collapsing system.

Try this book.

"Discover What You Are Best At" by Linda Gale.

It's a series of self tests you can finish in half a day, and then a list of jobs that use your particular skill set.

I never had a job I liked until I saw what the book suggested for me.