Yes @MDT Dont underestimate your strength. You are intelligent, thoughtful, caring, got travel, girlfriend, study and work under your belt. That is a lot of ticked boxes.
I have had to analyse ... mental illness from the ground up and dig down into its roots. Going back to your thread title.... I had to unpack the meaning of paranoia in my 20s and thought about it a bit over the years. Both my parents were hospitalised more than once and given the dreaded label in your thread title. In a way it has strengthened my understanding of some mechanisms of mental illness. I always gave mum plenty leeway for dealing with WWII stuff.
Self doubt is a thing. Most people experience it a bit of the time. I do. We can yoyo without or it can be paralysing, which is probably my main way of experiencing it. Maybe part of the trick is to cultivate some mantras or self talk to deal with it when it pops up, and it may keep popping up idk ... but something to keep the doubty trouty fishy times at bay ... and keep fear for when you really are in deep water ... does that make sense?
We need our fear antennae ... to survive the dangers in life ... that do exist.
You may be dealing with fear rumbling underneath ... rather than thinking it indicated something is wrong with you ... accept it as your personality's style of processing feelings ... rather than any pathologising BS. There maybe some trauma major or minor ... and it is natural and best if you do work through it ... and it may be just the way you are. I always thought mum had worse situation than me, as I had never lived in war, which in a way dismissed my own frightening experiences as a very young girl.
https://crucible4points.com/about-crucible-therapy/ just an approach that takes into account psychoanalytic and relational aspects of being. Never had the money for that kind of thing so kinda figured it out on my own on the cheap ... the thought that strikes me as relevant is the idea ... of emotions in a crucible and rumbling away ... changing over time ...
Great to talk.