People Who Don't Know They're Dead
by Gary Leon Hill
The premise of this book is that some dead people do not realize they are dead. They continue existing in a confused state and, seeking the comforts of a physical body, accidentally latch onto living humans. The living host then experiences mood swings, unusual cravings, and behavioral changes that are actually the hitchhiking dead expressing themselves.
Gary Leon Hill is completely serious about this.
The book is written as a self-help guide. It includes methods for identifying whether you are currently hosting an uninvited dead person, techniques for compassionately releasing them, and case studies of people who sorted out their inexplicable fondness for 1940s jazz once they found and evicted a confused WWII veteran.
The tone is warm, earnest, and entirely persuasive if you do not question the foundational premise. Hill writes as someone who has helped many people with this problem. He has a chapter on children, who are apparently more susceptible.
Whether you believe any of it is between you and the possibly-dead person currently riding around in your body.