What if even the anxiety you classify as 'mental illness' is also instinct, just with an unknown purpose? What if it's not an illness at all, just a misunderstanding? What if the anxiety is coming from the same place as intuition, or as part of it?
Obviously I don't know what you deal with, but it seems like you are very self-aware and have put a lot of thought into the matter. I only suggest exploring this other perspective because I think the words you choose to tell yourself about yourself are important. Your body will respond to what you say about yourself, positive or negative.
supposedly it's a chemical imbalance which could classify it as a mental illness. Intuition I haven't thought of but I did see a video before explaining how social anxiety is your flight or fight instincts getting triggered in safe situations, which would be a misunderstanding. When I was in a situation that caused anxiety I tried calming myself by saying I was safe, and it did actually work sometimes :)
You're right about responding to what I say about myself, but it is the easiest way to express to people how I feel
If telling yourself you're safe works sometimes, it could be your body responding to a trigger (possibly from a previous life, if you believe in reincarnation). Sometimes I think our bodies seem more like pets than our selves. They need love and care and to be told who they are, and sometimes how to behave, but they always learn sooner or later.