In the 21 May edition of the LRB there is a review of a book by Laure Murat called The Man Who Thought He Was Napoleon: Towards a Political History of Madness. The whole thing sounds extremely interesting but one anecdote struck me particularly.
The reviewer explains that in the period of the Terror in France a very common form of madness became a fear of being guillotined. This doesn't actually sound totally mad in the circumstances, now I come to think of it, but anyway the case that appealed to me was this one:
"Another celebrated case was that of the clockmaker, convinced that he had already been guillotined. Somehow the verdict had been reversed, but his head had become confused with others in the basket and he had been given back someone else's."
The oddest thing about this delusion is that I would have thought that you would think that you had been given back someone else's body, rather than someone else's head.