I think that I understand your feelings. I had the same periods of existential fear about most of the things that you had. Two of them I discussed in the post about AI failures levels which didn't got any comments to my surprise.

But it is also possible to have existential euphoria. First one I got than proved for my self the idea of quantum immortality. Second is that than I understood that I will become a god in my own branch of the universe. The last needs more complex explanation, which I would omit for now.

But as I became older I got less and less feeling from theoretical ideas.

Of course the most dangerous of all ideas is idea of death itself. Everybody knows it and nobody react on it. Most people got bulletproof for such ideas from 6 years old when they was told that they will die, and after it nothing will happened, and nothing can be done about it.