不知不觉
bù zhī bù jué
imperceptibly; unconsciously; unwittingly; unknowingly; not knowing and not feeling; without one's noticing it:
他们睡了好几个小时，不知不觉，东方已破晓了。 They had a good sleep of a few hours without their noticing it, until the east was already beginning to grow bright.
不知不觉已过了三个月。 Three months have passed before we knew it.
