WordNet sense 1 (as if struck dumb with astonishment and surprise):

dumbfounded, dumbstruck, flabbergasted, thunderstruck, dumfounded, dumbstricken

WordNet sense 2 (taken unawares or suddenly and feeling wonder or astonishment):

surprised

WordNet sense 3 (in a state of mental numbness especially as resulting from shock):

dazed, stupid, stunned

WordNet sense 4 (mentally confused; unable to think with clarity or act intelligently):

confused