Princess Alexandra of Bavaria was a noted author and translator in the mid-19th century. She also firmly believed that as a young child she had swallowed a grand piano made of glass.
For whatever reason, many historical descriptions of mental illness have something to do with glass. Alexandra dressed only in white (a hundred years before Tom Wolfe made it cool) and had a thing about cleanliness, but she is best remembered for the belief that as a child she had eaten a grand piano made entirely of glass. And that it was still in her stomach twenty years later.
Charles VI of France (known, for no reason I’m sure, as The Mad), believed that he was made of glass and would shatter if someone touched him. He had metal bars sewn into his clothing to prevent this tragedy.
This specific fear, known as the glass delusion, was apparently fairly common: Cervantes (of Don Quixote fame) wrote about it, as did René Descartes. And, of course, Blondie.