知しらない間あいだに

expression

before one knows it; without noticing; unawares

Describes something happening while one is unaware or not paying attention; often used for gradual changes or unexpected events.

• 知しらない間あいだに雨あめが降ふり出だしていた。

  Before I knew it, it had started raining.

• 知しらない間あいだに彼かれは部屋へやを出でて行いった。

  He left the room without my noticing.