While there are some Horror movies that have alluded to various religions, and have done them successfully (The Wailing), "Sleep" seems to presume the audience is already familiar and sympathetic with Shamanism and Buddhism, including their esoteric rituals and practices without any justification or explanation. As a result, those unfamiliar with these practices will find the character's behavior off-putting and their responses bizarre. For example, in one instance, the priestess starts ringing her bell loudly to deter the supposed demon possessing the husband. However, she also approaches the baby and starts to violently ring a bell against the baby's ears causing it to wail. Both the ML and FL, who are apparently skeptics at this point in the movie, don't consider at any point to perhaps engage this shenanigan without the baby? Rather, the delirious and sleep deprived FL becomes more convinced by the shaman's antics, while the ML gets slightly agitated and shields the baby, but does not assume that the unruly practice might either traumatize or harm the baby. At this point, the realism of the story is lost for me because none characters are acting as how normal people and purported skeptics would: bothered and protective.
When we get to final segment of the movie, there is an interesting dilemma of whether the protagonist is suffering from paranoia or whether her husband is genuinely possessed. While interesting, it was, unfortunately, poorly executed. To convince the demon to leave, the protagonist not only kills the neighbor's dog, but kidnaps the neighbor and threatens to drill a hole in the neighbor's skull. What is the neighbor's response to all these violent acts against her? That the demon should stop possessing the husband...
Initially, I thought, perhaps the neighbor was simply pretending to go along with the protagonist's hysteria to preserve her own life. But then, the neighbor begins to converse with the husband as if he were really her dad, begs him to leave, and promises she would perform ancestral rites for him. There is not a single indication that the neighbor is performing an act, but rather we see both the neighbor and the protagonist believing the husband is possessed, insistent, and seemingly justifying FL's previously fanatic behavior to expunge the demon.
For any rational person, whether religious or not, this is incredibly abnormal behavior and dialogue. Suppose you were a devout Jew, Christian, Muslim, Buddhist, Hindu, etc. and someone kidnapped you because the kidnapper believed your parent's spirit/demon was haunting her or her family member. Wouldn't the initial reaction always be: This person is insane; please stop her? Wouldn't you try to reason with the kidnapper when given the opportunity to? Apparently, not in this movie.
And without surprise, it turns out the husband was actually possessed..! Thus, the implied message in the ending is: everything was justified and peace has returned... Yikes.
There are other unconvincing behaviors in the movie as well, such as the wife's wanting to ignore and put up with her husband's strangeness because of an arbitrary signpost that he crafted: "Together, we can overcome everything!" Ah yes, that's why I should allow my husband near my baby even though he accidentally killed my fur-baby because, apparently, we can overcome this situation together by jeopardizing my baby's life? No pain, no gain; no risk, no reward! I genuinely don't understand what sort of rationale, if any, was in this writer's mind when creating this nonsense.
It's a shame because I think the movie would had a lot more potential if it went with a psychological than a supernatural direction, or if it was not written by a religious extremist, since the possibility that the husband acted as a demon (for he is an actor, though merely an extra) in the end could have been a perfectly tenable theory. That is, until it is squandered and crushed by every other character's reaction.
All in all, the writing is mediocre, the story was decent, the acting was great, and it had its thrilling moments. It is a fun movie, but it is far from outstanding.