Born of the Heretical Way

The protagonist is a mentally ill man suffering from delusions. In reality, he inexplicably transmigrates to another world. Whenever his consciousness transmigrates there, everything that happens is projected onto him exactly as it occurred. When he talks to people in the other world, his real-world self stares blankly into the empty hospital room and mutters nonsense. And while he is in the other world, events in reality are likewise projected there exactly as they happen. That eerie world is overrun by all kinds of ghosts, zombies, and monsters. So he is lost, unable to tell which is real and which is fake. Is it the bizarre and fantastical other world, or the seemingly ordinary real world where no one believes him?