One theory about nightmares is that they serve as exposure therapy for stressors. If your nightmares are too extreme, maybe you could set aside during the day to enter a calmer environment and try to review them without getting overwhelmed. It might desensitize you a little bit and make them less severe.
I haven’t had severe nightmares since I was a preteen, but when I did, they tended to be pretty stressful (being kidnapped, being abandoned, my friends commiting suicide in front of me, etc). I’m not sure exactly why they stopped, but I eventually ‘burnt out’, and I just stopped really caring about them.
Can’t say I turned out great, but I can say I don’t have nightmares anymore.
The issue with sonnet 3.5 is, in my limited testing, is that even with explicit, specific, and direct prompting, it can’t perform to anything near human ability, and will often make very stupid mistakes. I developed a program which essentially lets an AI program, rewrite, and test a game, but sonnet will consistently take lazy routes, use incorrect syntax, and repeatedly call the same function over and over again for no reason. If you can program the game yourself, it’s a quick way to prototype, but unless you know how to properly format JSON and fix strange artefacts, it’s just not there yet.