False Memory - Dean Koontz

Martie Rhodes is a happily married, successful video games designer, and a compassionate woman who, twice a week, takes agoraphobic friend, Susan Jagger, to therapy sessions; although each trip is a grim ordeal, it has also been a bonding experience that has brought the two friends even closer together.

Then one morning, Martie experiences an irrational fear of her own. She suffers a brief but disquieting terror of... her shadow. She sees something twisted in it, something not right. Other anxiety attacks quickly ensue... until Martie discovers she is afflicted with one of the rarest and most intriguing phobias known to psychology: autophobia, a fear of oneself. Because of the astonshing and terrifying ways in which this phobia manifests itself, Martie's life changes suddenly, radically - and her future looks dark.

Martie's husband, Dusty, is a rock for her. He loves her profoundly, and he becomes desperate to understand the nature and cause of her autophobia. But as Dusty comes ever closer to the terrible truth, he himself begins to exhibit symptons of a psychological disorder, even more unusual and frightening than that afflicting Martie....