HSK 7-9
不知不觉
bùzhī-bùjué(idiom) unconsciously; unwittingly
我们不知不觉聊到了深夜。
Wǒ men bù zhī bù jué liáo dào le shēn yè.
We talked late into the night without noticing the time.
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Appears across levels (7-9) in the HSK 3.0 word list.