What should I do about this line of thinking?
Acknowledge it and consciously address it.
I had to take blocks and a shovel away from my best friend last weekend because she was having an anxiety attack. Her brain was pulling up even the most minor of negative memories from the past. She was using those to 'measure' her 'worth' and she knew it was ridiculous, but her brain was telling her otherwise. Her brain wanted to keep digging into noncorollary context because of habit, not logic.
I asked her how items A, Q, I, and G were revelant to the here and now. There was no logical reasoning. By asking how the squash relates to the apple, it made her consciously stop digging. I was more than willing to lend her some blocks to build some steps to climb out of the hole. She just needed someone to listen and talk it out with.
She refocused away from the downward track and stepped back onto the facts. Anxiety is a chemical imbalance, it is inherited, she comes by it honestly, and it is not a weakness, just a feature of her neurotype. What her brain was telling her about her worth as a human being was a load of tripe. As anybody who knows her would tell her. Truly, she is someone you want in your corner in a tough situation.
She is one of the kindest and most trustworthy people I know, but she forgets to see how far she has come and all the work she has done. I've seen her progress, the effort she has put in, how much she has grown as a person emotionally. While she still struggles with anxiety, she knows she can reach out to a number of us and we will take the shovel. She knows she is worthy of the blocks we willingly give.