when he thinks the sun has gone out, why is Scrooge worried?

"Why, it isn't possible,'' said Scrooge, "that I can have slept through a whole day and far into another night. It isn't possible that anything has happened to the sun, and this is twelve at noon!''

Scrooge believes that he's lost another day, that the sun didn't rise, and it was twelve in the afternoon. After looking out his window, at the quiet scene below, he discerns that all must be well because the world below wasn't crazy with fear.