Memoirs of a Teenage Amnesiac by Gabrielle Zevin

If Naomi had picked tails, she would have won the coin toss. She wouldn’t have had to go back for the yearbook camera, and she wouldn’t have hit her head on the steps. She wouldn’t have woken up in an ambulance with amnesia. She certainly would have remembered her boyfriend, Ace. She might even have remembered why she fell in love with him in the first place. She’d know about her mom’s new family. She’d know about her dad’s fiancée. She never would have met James, the boy with the questionable past and the even fuzzier future.

But Naomi picked heads.