Before I Go to Sleep by S.J. Watson

Christine loses most of her memory every night when she goes to sleep. Sometimes she wakes thinking she’s in her twenties, sometimes even younger. She doesn't know where she is, or what has happened to her in the past several of decades. With the help of a psychologist and her journal, she begins to reconstruct her life and discovers just how vulnerable she really is.
Serious, strange amnesia in fiction is almost always a little too convenient. It's one of those things that happens all the time in books and almost never in real life (like the revelation that your father is not really your father). I picked up this suspense novel because of the compelling cover, but thought - boring, another amnesia story. Then I started reading and I could not put it down. It is definitely one of  my recent top recommendations for beach/vacation reading.