The Darkness of Dreamland - T L Bodine

When 7-year-old Nathaniel Weaver is kidnapped by his imaginary friend, the only person who can find him is his social worker.

Child welfare agent Adrian Montgomery lives a life of routine, reason, and careful compartmentalization. But his search for Nathaniel leads him through a door in reality itself, slipping into Dreamland: A faerie realm fueled by human dreams, where unseen monsters sweep through in the darkness to eat away at rational minds. Lingering too long in Dreamland means losing himself entirely, but escaping means finally confronting his worst nightmares -- literally.