not know what hit you

not know what hit (one)

To be extremely shocked, surprised, or confused by something. When my father passed away, I just didn't know what hit me. With this new strategy, our opponents won't know what hit them.
See also: hit, know, not, what
Farlex Dictionary of Idioms.

not know what hit you

be hit, killed, or attacked by someone or something without warning.
See also: hit, know, not, what
Farlex Partner Idioms Dictionary

not know what ˈhit you

(informal) be so surprised by something that you do not know how to react: You should have seen his reaction! He didn’t know what had hit him! OPPOSITE: see something coming
See also: hit, know, not, what
Farlex Partner Idioms Dictionary
See also:
  • not know what hit (one)
  • not have a clue
  • have a clue
  • see the light
  • see the light, to
  • begin to see the light
  • lose the thread
  • (one) doesn't know which way is up or down
  • lose the drift (of something)
  • lose the drift/thread of something