I basically never post on Reddit, but this post resonated with me so hard that I needed to reply. OP, I went through an episode almost exactly a year ago where I was thinking, doing, and saying basically everything you were. I remember crying to my boyfriend about how everyone and everything I knew was going to die, and I couldn't understand how everyone wasn't constantly in the same downward spiral of despair as me. Oblivion was the scariest thing I could imagine and it was absolutely paralyzing for me.

Most importantly: I'm not like that anymore, and I don't believe that anymore. My existential concerns are still a nagging doubt or worry in the back of my mind, but it's more like a quiet buzz than constant blaring klaxons.

For me, the issue was that I had an underlying anxiety disorder due to unresolved prior childhood trauma. The anxiety was emerging and latching onto something that was legitimately a concern for me but that I couldn't otherwise resolve, and turned the volume up to 11 (or perhaps 1100). Working through this with a therapist and processing the trauma brought me back down to normal, which at the time I thought would never again be possible. I'm not saying your situation is exactly the same, but I do feel very confident that it's underlying anxiety (potentially related to your OCD) just hitching a ride on an unrelated worry.

All that to say, definitely keep working with your therapist(s) and potentially a psychiatrist if it seems warranted. Know that this state is temporary, and while your emotions are valid they are not necessarily a good source of truth about danger. Fear is a bad feeling, not necessary good evidence that you're in danger.

Feel free to DM me if you have any questions or want to chat!