In 1786, Constanze fell ill and was bedridden. Wolfgang sat by her side and composed, while making sure no one would disturb his wife’s sleep. Suddenly, a valet clumsily entered the room and startled Mozart so much that he jumped on his seat and accidentally stabbed his own thigh with a knife he used to sharpen his pen.
He tried not to scream in order not to wake Constanze up and ran in another room. He was later healed by his mother-in-law. He never told Constanze.
[Source: Sophie Weber]