knock somebody sideways
knock (one) sideways
1. To impact one with physical force, either intentionally or unintentionally, resulting in pain, disorientation, etc. He wasn't going very fast at all, but it still knocked me sideways when the cyclist ran into me.
2. To shock, surprise, astonish, or bewilder one. The end of that trick always knocks the audience sideways. I love watching their faces as they desperately try to figure it out. It really knocked Stu sideways when Olivia announced she was leaving the company.