This is not the greatest horror movie but at least it had an interesting plot line. I liked that the horror element came from the growing doubt between a married couple. The clever thing that they did was the doubt was not one-directional but it changed throughout the film, which was quite unexpected. Another clever thing was that they used two different types of sleep disorders, narcolepsy and insomnia to describe (possible) possession and paranoia, which are common subjects in a horror film. Possession was so often done in Korean horror movies these days and thus I was hoping for something more different though. But still, overall a very interesting attempt.