It’s best to do DBT with a professional, but there’s a large community of DIY DBT practitioners out there. [1]
If your unable to investigate the source of some feelings (e.g. because your brain shuts down when you interrogate them) there is a new-ish practice for detangling your thoughts without all the interpersonal unpleasantness of Talk Therapy (that doesn’t mean it won’t be unpleasant in it’s own way).
It’s called Eye Movement Desensitization and Reprocessing (EMDR). Again, working with a professional is best, but it’s possible to be successful with a DIY approach. [2]
Disclaimer: I’m not a professional in any form of health, mental or otherwise. I’m just a happy self-administered DBT & EMDR patient :)