Definition
To be suddenly shocked or confused by an unexpected negative event, leaving one unable to react.
震惊莫及
When he found out he was fired, he didn't know what hit him.
当他发现自己被解雇时，他完全不知所措。
The company experienced such massive losses, they didn't know what hit them.
公司经历了如此巨大的损失，他们完全不知所措。
She never expected this to happen, so when it did, she didn't know what hit her.
她从未预料到这件事会发生，所以当它发生时，她完全不知所措。