I have been hearing fantastic things about this book. It's sold in something like 35 countries. Interestingly, when I saw the writer's name, SJ Watson, I assumed it was a woman, since it's usually women who choose to hide behind initials. Maybe he did it because it's told from the POV of a woman?
Here's a partial description: "Memories define us. So what if you lost yours every time you went to sleep? Your name, your identity, your past, even the people you love—all forgotten overnight. And the one person you trust may be telling you only half the story. Welcome to Christine's life."
I feel like playing hooky!