信じられないくらい驚いての英語

I am struck dumb with astonishment―I am dumfounded―（他動詞構文にすれば）―Astonishment deprives me of my power of speech.

It's not surprising.

faint with fright

I'm so surprised I still cannot believe it.

not alarming

a feeling of wonder

I was stupefied with astonishment.

startle with amazement or fear

to surprise excessively

What was （not）his surprise on finding that!

I was really surprised.

the condition of being greatly surprised

surprise greatly

to a stupendous degree

He was frightened out of his wits.

extremely alarming

surprisingly

a total surprise

to be shocked

a surprising rumor

to be greatly surprised

of a person, being in a startled state

I was very surprised

a shocking surprise

to be horrified―horror-struck

I am positively surprised.

I nearly fainted!

I am not in the least surprised.

overcome with amazement

not surprised or expressing surprise