thunderstruck
So shocked or amazed that you cannot move or speak.
Thunderstruck means stunned or shocked into silence, so surprised that you can barely move or speak. The word comes from the image of being struck by lightning: frozen in place, mouth hanging open, unable to think clearly.
When your teacher announces a surprise field trip to somewhere amazing, you might stand there thunderstruck. When a basketball player makes an impossible shot at the buzzer, the crowd falls thunderstruck for a moment before erupting in cheers. When you open a gift you never expected, that feeling of total astonishment is being thunderstruck.
The word captures that specific moment when surprise overwhelms you completely: your brain needs a second to catch up with what just happened. You might be thunderstruck by good news, like winning a contest you'd forgotten you entered, or by something troubling, like discovering your best friend moved away without telling you. Either way, the feeling is the same: you're temporarily frozen by the force of the surprise, as if an actual thunderbolt had knocked the thoughts right out of your head.