I don't want to be left alone with existential anxiety either and I'm an adult. I had it since I was a child and I never even dared speaking to my parents about it because I knew they would just tell me to go back to my room and stop the "behavior". So I curled up alone in the dark panicking on the inside but not daring to even move so I wouldn't upset my parents.

Days are easy, you are distracted. Maybe too distracted? Like above, maybe deal with the thoughts in a safe environment when the sun is up? When it's dark and you're alone with yourself it's hard. I still have times I totally dread going to bed.

I don't think when it is deep rooted like this, you can't just train him to behave.

I found comfort in some books about other people's thoughts in the same matters. It felt like company because they had thought the same thoughts I did. Maybe you guys can find some books like that.