Unique to the late Medieval period, the Glass Delusion is rarely (if ever) seen nowadays. It was a psychiatric disorder in which the person believed that they were made of glass and fear contact with other people or objects in fear of shattering. King Charles VI of France was one of the few royal sufferers from the disorder (you can look him up to find stories related to him and his disorder). It was common enough that literature of the time often referenced it. Typically the 17th century is referenced as the end date of the Glass Delusion. For some reason around that time cases stopped being recorded. How absolutely fascinating–especially since there is still so much we have to learn about it.
If you want to read or hear more about the Glass Delusion, check out the Stuff You Missed in History Class article or podcast about one of the royal cases of the disorder, Princess Alexandra of Bavaria who famously believed that she swallowed a glass piano.