What moments do you see the key characters coming to terms with issues surrounding the definition of mental illness?

This happens at different times throughout the novel. Certainly Chief coming out of his fog and communicating again is important for him. McMurphy was never mentally ill to begin with. You can check out the other characters below:

http://www.gradesaver.com/one-flew-over-the-cuckoos-nest/study-guide/character-list/