It is true.
Writing a novel is like giving birth. The author creates lives, builds a story around these characters, uses words to construct a world in which these characters live and interact. The author can spend a month to several years writing a novel, living with these people who become quite real over time, manipulating them, directing them, leading them to the conclusion of the novel. And then you reread the pages, edit, rewrite, add or subtract material, fine tune the characters and the story. Then off it goes to be published- and the feeling of loss and separation sets in. It's similar to empty nest syndrome, or post partum depression. The author has created an entity out of their own self, their own imagination, heart, and soul. And then the cord is cut and the book goes off into the world and the author worries whether or not the book will be successful or will flounder. It's wrenching yet exhilarating. We wish for our "babies" to be successful and we are disheartened when they fail.
As I anticipate the final proof version of Black King Takes White Queen I feel aimless at no longer having those characters in my day to day life, anxious about whether or not it's good enough this time, and nervous about if it is good enough, how it will be met by the reading public.
Although I have written 9 story collections and 11 novels, a young adult novel and a young reader book and have been through this post novel depression numerous times I still experience the separation that comes with a project completed and about to launch.