"Shock" is a feeling of extreme suprise. When you're "in shock", you can't believe what's happening. You can't speak or move.

Of course, people sometimes exaggerate their feelings of surprise by saying that they were "in shock" about things like the price of a haircut:

When they told me how much it was going to cost, I was in shock.

It's common to combine "in shock" with the adjective "total":

She looked like she was in total shock.