In those days, indoor plumbing was almost 'unheard-of'. [=very few people had indoor plumbing]
The students' concerns 'went unheard' [=were ignored] by the school's administration.
It's not 'unheard-of' for a patient's condition to improve this quickly.
(..) How is that possible? Because l... I told her the truth. - Oh, my God. - Okay. - It's unheard of. - She asked me to. So you lie. - What did you tell her? - I told her that she was pretentious. Pretentious? (..)1991 TvShow: Seinfeld Title: The Truth Season: 3 Episode 2