To stupefy someone means to shock or stun them into silence or stillness.
When we say that something or someone has stupefied us, it usually means we've been surprised or amazed so much that our normal reaction has stopped working. Imagine being at a concert and the music starts blasting out of nowhere - you're likely to stop in your tracks, mouth open, with no idea what to do next. That's kind of like being stupefied. It can be a person, an event, or even just a thought that suddenly hits us and makes our usual thinking freeze up.
To dull the senses or capacity to think thereby reducing responsiveness; to dazzle or stun.
