The dictionary dictators amongst others define the word gobsmacked the following way…
gob·smacked
1 ˈɡäbˌsmakt/
adjective BRITISH informal
adjective: gobsmacked
utterly astonished; astounded.
With reference to being shocked by a blow to the mouth, or to clapping a hand to one’s mouth in astonishment.
Not me, while I have no doubt that is the correct definition, I would amend it to include a second: