Before I go to Sleep by S. J. Watson

Christine looses all memories when she sleep.  She wakes every morning with no idea who or where she is.  Her husband Ben reintroduces himself and tries to make her safe in her world.  Her doctor urges her to keep a journal but a message in the front of the journal tells her to keep it a secret from Ben.  She does not remember why.  Ben discourages her from seeking medical treatment for her memory loss.  She is not sure why.  One of them is lying to Christine.  How do you discover the truth when your world starts over every day?  This is not great literature but I could not put it down.