Slang for an ailment caused by missing someone, or “simping for someone”, most likely called Ethel. The reason the name “Ethel” was picked was because it originated from an elderly man who had strong feelings for his partner (named Ethel). Ethel Syndrome can be used interchangeably with the popular internet slang “simp”.
I like this girl so much, I must have a case of Ethel Syndrome.