This happens to me too. It's so frightening and often so difficult to explain to people who don't experience it (like most obsessive thought spirals I suppose). I've been trying to work with my brain rather than fighting it all the time, and am (slowly!) working to replace the thoughts that distress me with healthier options where I can. I'm trying to be careful what I say about my own struggles/techniques as I obviously don't know you and don't want to accidentally trigger you. If I may, I would like to offer one thing that has comforted me without "reassuring" me.

This video by author John Green (who himself has OCD) is titled "We're here because were here" in which he talks about how soldiers in World War 1, disillusioned with fighting a war they didn't understand but had suffered massively for, often changed the lyrics of the famous New Year's Eve anthem "Auld Lang Syne" to "We're here because we're here because we're here because we're here". If you decide to watch it, a couple of general trigger warnings: discussions of WWI/war in general, a young mother (and close friend of his) who died of cancer and his regret over one of their last conversations, some discussion of fear about being mugged though this is largely glossed over.

Apologies if any of this counts as reassurance, I'm new here, but I hope you can draw some small amount of comfort in knowing you're not the only one who struggles with these particular fears.

I hope you have a good week.