Rereading your comment--a part I didn't respond to: One of most influential writers of my youth was Miguel de Unamuno. If you are not familiar with him, he wrote a long, long essay called the Tragic Sense of Life(translated). He addresses your point, about the Buddha and awareness. While Unamuno is considered to be an existentialist, a "modern" thinker, he really starts at the same place that led to Buddha's awakening. I've no doubt many a psychiatrist would have viewed the despair of Unamuno and Buddha as pathological. But these men just had the courage to look into the abyss and come out with a way to go on.
I don't have great insight into "mental illness"--I do think throughout history it has mostly been normative, and also used for political and social coercion. But there are people tortured by a brain that is affected by a disease process. Right now we can't help those people, because we don't understand the process. Maybe the tools of science can change that.