Before I Go To Sleep by S.J. Watson

Christine wakes up every morning with an unfamiliar man. She looks in the mirror and sees an unfamiliar, middle-aged face. And every morning, the man she wakes up to must explain that he is Ben, he is her husband, and a terrible accident two decades earlier decimated her ability to form new memories. But it's the phone call from a Dr. Nash--a neurologist who claims to be working with Christine, without her husband's knowledge--that directs her to her journal, hidden in the back of her closet. For the past few weeks, Christine has been recording her daily activities and rereading past entries, relearning the facts of her life as retold by the husband upon whom she has become completely dependent. As the entries accumulate, inconsistencies in Ben's account jump off the page. What was life like before the accident? Do they have a child? And what exactly was the horrific accident that caused such a profound loss of memory? The closer Christine gets to the truth, the more unbelievable it seems.