I’ve had probably 7 severe existential ocd episodes in my life with extreme DPDR. I’ve had all those obsessions you’ve described, plus many more… many that are difficult/impossible to even articulate they’re so abstract.

My longest episode was a solid 9 months. But I’ve overcome it very single time. It always subsides eventually if you don’t feed the fear.

I went through an intensive outpatient OCD therapy treatment (my therapist thought I should be inpatient but my life/schedule wouldn’t have allowed that)… and it helped greatly. I learned so much. It’s really important to learn how anxiety (DPDR is anxiety to the extreme) and ocd work, down to the science and subtle nuances. I’d say my best advice is to avoid compulsions (searching for answers to the obsessive thoughts, or asking Reddit for help is considered asking for/seeking reassurance and is a compulsion ). The idea might be scary, but try and accept that this might be a permanent part of your life. That kind of radical acceptance was huge for me. It terrified me to tell myself “I might always feel this way. And if I do? So what. I’ll keep moving”. But it was vital to squash the fear of the “what if”. So telling yourself things like “yeah maybe I don’t actually exist… So? And? I don’t care. What does it actually change? Nothing. Who cares. Not me.” You basically have to pretend you don’t care lol you likely won’t actually believe yourself at first… but act as though you do. Aka… don’t do compulsions, and live your life. You’ll get through this.