How does Ken Kesey challenge societal notions of sanity and insanity? Who is sick, according to Kesey?

In One Flew Over the Cuckoo’s Nest, author Ken Kesey consistently challenges our notions of sane and insane in a variety of ways.
First, Kesey’s protagonist, McMurphy, gains admittance to a mental hospital by faking insanity to avoid prison. If one person can fool the hospital administrators, it raises immediate questions in reader’s minds: How many other patients do not live with a real mental illness? Can the staff really tell the difference?
Continuing with this theme, Kesey reveals that Chief Bromden, another main character, has also fooled the hospital staff. He has been faking being deaf and dumb (an outdated medical term for one who is unable to speak) for years. Kesey also implies at several points that Bromden has been “cured” of his disabilities. This is indicated when the chief talks about “seeing clearly,” without the fog that clouds his vision before McMurphy arrives.
Furthermore, Kesey exposes the use of shock treatment (electroconvulsive therapy) and lobotomies, which were common treatments throughout the mid-twentieth century. After reading about these treatments (or seeing them on the screen), one might wonder if the hospital personnel are the insane ones.