We've all had that moment when you see or hear something and wonder: am I going crazy? In this episode, TED speakers share their experiences straddling the line between madness and sanity. Neurologist Oliver Sacks explains a peculiar condition called Charles Bonnet syndrome - when people of sound mind experience lucid hallucinations. Law professor Elyn Saks shares stories about her schizophrenic episodes and how she was able to rise above her grave diagnosis. Plus, author Jon Ronson goes psychopath spotting, and wonders who among us is truly completely sane.