catch oneself up short

[Bushwhacker]

Does catch oneself up short mean something like "restrain oneself", or rather "gotten by surprise", not expecting what is happening"?

Thanks a lot

 

[Kondorosi]

catch up short - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.

 

[Bushwhacker]

catch up short - Idioms - by the Free Dictionary, Thesaurus and Encyclopedia.

Context is that someone proposes to do something to somebody else, this one says not, and proposes something different and, while saying all that, he becomes aware the other is staring at him and catches himself up short.

Does it mean he didn't expect being watched like that? That he was unprepared for this gaze?

Thanks