creep up on somebody/something phrasal verb ( see also ↑ creep )
1 . to surprise someone by walking up behind them silently:
Don’t yell – let’s creep up on them and scare them.
2 . if a feeling or idea creeps up on you, it gradually increases:
The feeling she had for Malcolm had crept up on her and taken her by surprise.
3 . to seem to come sooner than you expect:
Somehow, the end of term had crept up on us.