The state of being so shocked, so tired, or so bored that your mind stops working properly. It is the noun — the condition itself — where 'stupefied' is the person and 'stupefy' is the doing. Its main use today is about astonishment: you stare, you cannot speak, you cannot take in what just happened. 'He listened in stupefaction.' But it holds a second, duller sense that comes from the same root: the fog of a mind numbed by drink, by drugs, by exhaustion, or by hour after hour of nothing to think about. This is a rare and bookish word. You will find it in novels, in older writing, in translations of European fiction; you will almost never hear a friend say it. In ordinary speech people say shock, amazement, disbelief, or simply 'I couldn't believe it'. If you use it in an essay, expect it to feel a little grand, which is sometimes exactly the effect you want, and sometimes not.

目瞪口呆、神智麻木（書面語）