I failed and I feel so guilty
That is a normal emotion to feel after you fail!
I fear that I can't fully trust myself any more.
Failures are a normal part of life. Accept your failure, and learn from it.
I feel that I'm dumb. I feel like I can't fully trust myself anymore. I can't think all too well. I'm losing my mind and sanity.
Just try to use it as a less and then grow from it! I think that it will help in the long run!