Oof. That is tough, @Fojaje.
Is your sufferer open to talking, when he's in a more calm state? Re-affirming boundaries, keeping yourself safe, even emotionally, are things you absolutely have a right to.
Knowing the "why" behind behavior like that doesn't help when there is nothing to be done for it. My own sufferer would berate and belittle me for having a degree in a liberal arts field, instead of something "useful" like STEM, or a trade. He's scream at me about politics. Intellectually, both of these things are something we agree with each other, but when he is in a hyper-aware state, somehow the vilification on me starts. And, the more he descends into this spiral, the more paranoid he gets, and farther from his own beliefs.
Sadly, when our sufferers aren't addressing the root of the problem, there is little WE can do, beyond taking care of ourselves.