And then I picked up Flip
Here's the description: "One December night, 14-year-old Alex goes to bed. He wakes up to find himself in the wrong bedroom, in an unfamiliar house, in a different part of the country, and it's the middle of June. Six months have disappeared overnight. The family at the breakfast table are total strangers. And when he looks in the mirror, another boy's face stares back at him. A boy named Flip. Unless Alex finds out what's happened and how to get back to his own life, he may be trapped forever inside a body that belongs to someone else."
This was a great book - part mystery, part a meditation on life and death and the concept of the soul. Alex was easy to identify with. I read it in great gulps. Highly, highly recommended.