I used to think I had brain damage when I was at secondary school, because the lessons weren't taught clearly enough for me so rather than blame them I thought I was just feeling very confused and having difficulty focussing. I also developed a problem following TV programmes, and I was aware that my short-term memory kept failing and impaired my capacity to think. A few years later I noticed that poor concentration was said to be a symptom of schizophrenia. I'd also seen a friend's behaviour after a "nervous breakdown," when he became very indecisive and didn't quite respond right to social greetings and attempts at conversation, and I saw myself in that behaviour, because I didn't seem to make quite the right responses either when I was with people, I felt like I was isolated in a bubble.
But I've never suspected myself of being delusional or a danger to self or others, it was purely a matter of whether my brain had a proper grip on things. I've always liked harmless eccentricity in people, so anything I did that seemed unusual, that was just my colourful character, which I figured was much more interesting and imaginative than just following convention.