I’d try to break down the problem into more manageable chunks. Existence is pretty huge and you can’t really work on all of it at once.
I have a pretty specific idea of what it means to exist. I have goals, I try to accomplish those goals, I succeed, I pick new goals, rinse, repeat until I’m dead.
This is more of a ‘map’ of things where if I’m dissatisfied in an area of my existence, I can go look at the map. Generally I see that I’ve wandered off the course I’d tried to set at some point. So I’ll work back to where I used to be and figure out how to get back to a productive place.
It sounds like you might actually be experiencing a known psychiatric disorder. You might find a consultation with a professional to change your life. I see a psychotherapist every week. I look at her as a “primary care physician” for my mental life. Talk therapy is really useful and I think everybody should do it.
You should find someone you like and that you can rely on. Most people only deal with mental health professionals in a non-voluntary context, so it’s easy to get the wrong idea about what psychology is all about.