Knock sb sideways/for six British Australia Verb + object/complement informal
To make someone feel very shocked, overwhelmed, upset or ill
What he said knocked me for six.
The decision my parents made really knocked me sideways.
The verb "knock" should be conjugated according to its tense.
To punish someone or something harshly
He's a really strict teacher, so he'll definitely lower the boom on you if you don't do your homework.