"Mental illness" is a term that works for many people, but to me the term "emotional vulnerability" feels kinder. I suspect it is when we humans have used outdated/ineffective defenses (to protect a vulnerability or two), that we end up with a full-blown psych illness, complete with diagnosis.
Professionals often tell those of us with "mental illness" diagnoses that we simply have faulty biochemistry. Alas, they have yet to "measure" mine. They simply prove it indirectly with medications that have powerful side effects. Today I suspect normies have unique biochemistries too, also unmeasurable. I just know that I am a valid part of the same human race, and just like any normie, my behavior (emotional mastery or lack of), sleep hygiene, spirituality, diet and exercise--can greatly affect biochemistry.
For me, attributing my "emotional vulnerability" to sheer biochemistry takes away my power, a good bit of hope and much of my responsibility. It can cause me to be more apathetic as well as more afraid of relapse. If instead I see that triggers are part of my biochemical/emotional vulnerability, then I find that I can make choices that help me handle my "uniqueness" in ways that are kinder and healthier. New living skills help me deal more comfortably with my triggers.
I am grateful that program has helped me live at greater peace with a mental health system that certainly disagrees with me on many points.
A better way of living is really the main goal of my life--not disagreement with the professionals. Program helps me to stay focused on that.