Death's Pale Flag book by  Gary Simonds

In this Literary Titan Book Award Winner, A highly-successful brain surgeon begins to encounter ghosts.

Brain surgeon and unlikely war hero, Ryan Brenan, has it all. A booming practice, a beautiful home in an idyllic setting, and a happy loving family. Then, the apparitions begin. Subtle at first, but soon there's no doubt about it, he's seeing ghosts, spirits, the undead. Of course, he could just be going nuts, cracking under the pressure of his constant exposure to death, mayhem, and tragedy. But, he believes he has proof that the ghosts are very real, and that they are specifically haunting him.