I like using the word ‘winced’ when writing about someone being in a state of disbelief, although that necessarily isn’t the same as being startled. I also think I may have described being startled by ‘a feeling of slow motion’ or ‘as though she just saw a ghost’ (cliche, I know, but it does paint the picture well) I may as well say’my jaw dropped’ while I’m at it.
And I’ve personally been startled to the point of peeing my pants (when I was attacked by bees), so that isn’t an unrealistic description for ‘startled’, either. I just read a book where when referring to getting caught doing something she wasn’t supposed to, the author said, ‘instantly felt like I had to s***.’
Or like Georganna said, instead of coming up with a gasp you could come up with a creative way of the person not breathing. Couldn’t get air in or out or my breathing momentarily froze.
Here are a couple of others that I’ve used:
I was so scared that the top of my head felt hot.
In such shock my ears were blinking and it seemed as though sound changed.
A slow motion “OOOOHHH NOOOOOOO.”
Felt like I was dreaming. It couldn’t be real. This can’t be happening.
The sensation of lava flowing through my blood.
So shocked that my hands and head were tingling.
As you can see I’ve experienced a lot of shock in my life. Ha!
I’ve found it helpful and thought provoking (believe it or not) to read comics when finding ways to draw strong emotion with words. It has helped me come up with ideas just by seeing the look on cartoon-like faces. Even when I imagine them in my mind it can inspire the right words.