Fetching details from the dictionary...

dumbfounded; overcome with surprise; in blank amazement; in a daze
突然の解雇通知に彼は茫然として言葉を失ってしまった。
Stunned by the sudden dismissal notice, he was left speechless.
火事の跡を目の前にして住民たちは茫然と立ち尽くした。
Seeing the aftermath of the fire before them, the residents stood in blank amazement.
茫然自失の状態から立ち直るまで数か月を要したという。
It is said that it took several months to recover from the state of blank shock.