You're right about that. I was in such a situation: I had strong feelings of anxiety, sadness, low self esteem. I went to a psychologist & psychiatrist and got a bit anti depressive medication, many books to read, meditation exercises, mindfulness. All these things were good and helpful, and I guess in most cases it's what's needed.
But nothing of all that totally helped; I still had this sadness and anxiety and lack/absence of self confidence.
Then many years later turns out I have an illness, hypothyreosis, that causes this. And medication (levothyroxine) made all this go away, and I'm a different person nowadays.
> who you are can absolutely be changed by [...] circumstances [...] illnesses
That's very correct. I've been two different personalities — one sad, anxious, withdrawn, another happy and social. It's weird what hormone levels can do to the brain and who one ... who one is? one's personality.
Anyway, if someone has depression and anxiety feelings, and meditation and self help books won't make that go away — then, a blood sample test, it's just 5 minutes. (Well, plus bus / subway / something to the health clinic.)