不知所措的英文怎么表达?

lost one's composure

at one's wits end

at panic

at a loss简单易记…

at the end of one's wits
at a loss
lose one's head

Totally embarrassed and don't know what to do.

embarrass直译为尴尬，这里就是局促不安、窘迫的意思。
不知所措是成语，外国人没有这成语，所以只能按照意思翻译成不知道该怎么办。

i'm speechless 或 i'm at a loss 都行