Do mental illnesses have certain eras? When we look at history, it seems like they do. There was the famous dancing sickness that struck medieval Europe. And then there was a strange delusion, first experienced by a king, in which the sufferer thought they were made of glass.

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In 1392, King Charles VI of France's brother Louis took a liking to a woman not his wife, forcing Charles and his army to ride out and fight the army of a French duke. On the way, in the punishing heat, Charles was stopped by a mysterious old man, clad in white, screaming that the king had to turn back as he had been betrayed. Soldiers chased the man away, but Charles' nerves were clearly disturbed, because when a page accidentally made a clanging noise with his helmet, the king turned on the company, screaming that he had to kill the traitors, and struck down one of his own knights. After a lot of screaming and confusion, Charles seemed to be sure that Louis was the traitor, and attacked him. It took several knights to restrain the king safely.

Maybe Charles had had the right idea. Some years later, when Charles and Louis were at a ball, Charles decided to come with some friends in costume. The costumes were that of "wild men," and were made by covering the men entirely in linen, covering the linen with pitch, and covering the pitch with yellow flax. As a precaution, all the torches in the room were moved to one side before the men came in. When they did, Charles moved off from the group for a moment to flirt with a lady. Louis, claiming that he wanted to find out who the men were, grabbed a torch, carried it over to the men, and thrust it at one man's face. It takes no imagination to guess what happened. All of the men except the king were burned.

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Immediately after each of these incidents, and then increasingly over the next few years, the king went into strange "spells." He would rage at the people around him, grow paranoid and fearful, have to be restrained during "fits." During these spells that could last for days or months, he would stop caring about personal grooming to the point where his servants eventually had to cut him out of his clothes. Although Charles treated his brother well โ€” in fact Louis was appointed as regent during the king's times of illness โ€” perhaps some subconscious anger surfaced. During his spells the king grew passionately fond of Louis' wife. Because she could calm him down when no one else could, she was constantly by his side.

Modern doctors are hesitant to positively diagnose historical mental illness. There's good reason not to make conclusions before at least meeting the patient, and there are all kinds of reason why surviving records are biased and inaccurate. That being said, Charles VI, and his grandson Henry VI, are frequently diagnosed with schizophrenia. This mental illness is still around today, but Charles VI seemed to have something else as well โ€” something that today is called "glass delusion."

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When he was unafflicted, Charles VI was a sportsman who was rarely found indoors; he liked exercise and motion. When his spells were upon him, he became a different man. He would sit in a room, motionless, for hours. If he did move, he did it with extreme caution. Questioned about this, he claimed that he was made of glass, and one wrong move would shatter him.

This belief was not specific to Charles VI. It was, oddly, specific to time period of the 15th century through the 17th century. For about 200 years, people around Europe suffered from the delusion that they were made out of glass and that they would shatter if they moved incorrectly.

It may have gotten a jump start with Charles, as royal diseases gain a certain aristocratic mystique no matter what they actually entail. The glass delusion slowly gained popularity, becoming more and more common until the 1600s, when it turned into a genuine cultural phenomenon. The many cases of the illness was noted in books like The Anatomy of Melancholy, but it became part of popular culture as well. Miguel de Cervantes of Don Quixote fame wrote a play about the disorder called The Glass Lawyer. Rene Descartes mentioned the glass delusion in Meditations on First Philosophy, the text in which he proves the existence of god. People wrote satirical poems and stories about the disorder. It wasn't just known, it was famous.

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And then it stopped. While there are occasional people who have delusions in which they are objects made of glass, there is no longer a real "glass delusion." Or perhaps there was never a real glass delusion. Certainly plenty of very smart people documented it. And it stayed around for over 200 years. But how can a mental disorder simply vanish? Have people changed? Has the era changed? Or has the way we express illness changed?

[Via History of Psychiatry, Blood Royal, Medieval France: An Encyclopedia]