BEFORE I GO TO SLEEP by S. J. Watson, 2011.

One of those thrillers that just takes hold and won't let you go! Fifty-something Christine Lucas goes to sleep every night, and the next morning discovers all her memories are gone. Totally. She has to begin again each day to piece together her past. She's been told she's an amnesiac due to an accident years before when she was in her twenties. Unknown to her husband, Ben, she's seeing a doctor, who advises her to keep a journal, but recommends hiding it. Writing in it and then re-reading it every day, spurs more feelings and memories--of a child, of having a loyal girlfriend, of publishing a novel. And as more memories come back in dreams and sudden flashes, Chris becomes more aware that everything is not as it seems, that Ben is not telling her the whole truth. Compelled to find out her past, she becomes more determined to discover the truth about her life, but realizes there's an element of danger involved as well, as someone doesn't want her to remember everything--at least not in the way it actually happened. Watson keeps the pages turning with intense writing, high suspense, and an unexpected conclusion. Totally absorbing and riveting.