HSK 7-9
废寝忘食
fèiqǐn-wàngshí(idiom) to skip one's sleep and meals; to be completely wrapped up in one's work
科研人员为了实验废寝忘食。
Kē yán rén yuán wèi le shí yàn fèi qǐn wàng shí.
The researchers became so absorbed in the experiment that they neglected sleep and meals.
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Appears across levels (7-9) in the HSK 3.0 word list.