Daily Chinese Idiom Guessing Game
A sudden and dramatic turn for the worse; a situation rapidly deteriorates.
形容形势或文笔等突然转变，并且很快地顺势发展下去。
叶剑英《伟大的战略决战》由于迅速而顺利地取得了辽沈战役的胜利，就使全国战局急转直下，使原来预计的战争进程大为缩短。”
The stock market was booming, but then it took a sudden turn for the worse.