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.
Learn the next connected idiom: 急转直下 (jí zhuǎn zhí xià) → 下落不明 (xià luò bù míng)
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