Recursion by Blake Crouch

At first, it looks like a disease. An epidemic that spreads through no known means, driving its victims mad with memories of a life they never lived. But the force that’s sweeping the world is no pathogen. It’s just the first shock wave, unleashed by a stunning discovery—and what’s in jeopardy is not our minds but the very fabric of time itself.
 
In New York City, Detective Barry Sutton is closing in on the truth—and in a remote laboratory, neuroscientist Helena Smith is unaware that she alone holds the key to this mystery . . . and the tools for fighting back.
 
Together, Barry and Helena will have to confront their enemy—before they, and the world, are trapped in a loop of ever-growing chaos.