.
I have.
It was Hostage to the Devil (1992) by Malachi Martin. The book is still in print. It is an allegedly factual account of five modern exorcisms.
You could argue that my fright was due to having been raised Roman Catholic... and you might be correct. Today I am a skeptic and free thinker. I do not believe in the supernatural. But Martin's serious descriptions of demonic possession and discussion of the circumstances that make one vulnerable are chilling. And, frankly, the accounts in this book haunt me to this day.
The book is allegedly fact and not fiction. I must say I have never been so affected by a story of the supernatural whether it be fact or fiction.
So have you been seriously frightened by a book?