Sci-Fi thought of the day

So I was watching an episode of Star Trek: The Original Series, the episode in particular was The Menagerie: Part I . I was watching it on blu-ray with the updated digital effects and the bonus material turned on. During a break in the bonus material one line came through from the Commodore asking Kirk hows does he know that Spock hasn’t gone mad?
That got me thinking. What would insanity look like in a Vulcan? Of course the easy answer is that he starts getting all emotional and such, but I think there is a more intriguing answer to the question.
Vulcan are all about logic, but logic is only as good as your premises. If you have a false premise you will reach a faulty answer by logic. (this may be part of the Vulcan tradition of foregoing lies. A false premise is a very dangerous thing.) What is one form of insanity for Vulcan is being unable to determine what is a false premise and what is not? That would lead a Vulcan who thinks he is pursuing a very logical course to be doing almost anything.