Where in the World is Sabrina Spellman? by Paul Ruditis
Sabrina is exhausted from all the studying she's doing for exams and so casts a little known spell to keep her awake. But Sabrina soon discovers that there is a terrible side effect to her spell - everyone she speaks to instantly falls asleep! Luckily there is a remedy for the spell's effects, but to make it work, Sabrina and Salem have to follow a crazy list of clues which sends them on a scavenger hunt around the world.