A hundred and fifty points lost. That put Gryffindor in last place. In one night, they'd ruined any chance Gryffindor had had for the house cup. Harry felt as though the bottom had dropped out of his stomach. How could they ever make up for this?
I can find these phrases on the web: bottom drops out, bottom drops out of the market, and bottom drops out of one's world. But I can't find "the bottom had dropped out of his stomach" anywhere. What does it mean in this context?