Responses
To put it simply: Sebastian literally scared Ciel back to his senses. That's what he meant by terrible wake up call. LOL. You ever read the Artemis Fowl and the Atlantis Complex book, that might help explain it a little.
Ciel is comparing Sebastian's 10 second horror movie to how he- Ciel -is usually woken up. And as Caitrona said, Sebastian scared him so bad, it brought Ciel back to his old self.
It's been bugging me for a while, What does Ciel mean by wake up call?
http://www.mangago.me/read-manga/kuroshitsuji/an/v18/c095/pg-19/