Your brain was still pretty good in making movie plotsWell, then you haven't met me.
After surgery, I developed a condition called ICU Psychosis. I heard voices that could not have existed (I believed that I heard a baby crying so desperately that I made my wife go check). I heard messages in the various beeping of the machines and heard people communicating with each other through my oxygen mask. I also watched an entire movie* that not only did not exist but the television I thought I watched it on didn't exist, either.
At the time, I was perfectly convinced of my own sanity and of the malicious intent of all those around me. I tried to choke my wife to death (but, since I was confined to my bed and as weak as a newborn, she just took a step back).
Luckily, ICU Psychosis is a temporary condition that fades when the patient gets normal sleep and sufficient non-monotonous stimulation. It's a strange position to be in. I remember things that could not have possibly been true, I remember believing them, and I know now that they didn't happen.
In my experience, the psychotic or schizophrenic person is the absolute worst judge of whether he or she is sick.
*The plot was that there was this young Indian man who would scam rich people out of their money by promising to put their daughters in a movie he was directing. Then, when he falls in love with one of his marks, he has to actually produce an entire Bollywood movie to stay near her.
Actually, I can understand, that, in really extreme situations (different from what Eleanor Longden explained), the brain stops functioning normally. But, even in such cases, it can be difficult for another person to separate truth from exaggeration.