The genius, center, heart, and terror of this film lie in the realism of the performances.
The actors who portray the couple are so convincing and so natural, you feel as if you are watching an actual homemade video.
They do not follow the usual “shaky-cam movie” model of acting in which the performances often try so hard to be “real” that they are over-done and come off as a cheap imitation of as what is assumed would be somebody else’s reaction to that scenario. Contrary-wise, we believe as an audience, that “Paranormal”’s characters are true to themselves, and the decisions they make and the things they say are true expressions of how the actors themselves would feel if they had been placed in the same situation.
Thus, instead of feeling like you are watching actors in a movie portraying someone else, you feel as if are watching two actual people in an actual haunting scenario.
You recognize that everything they say and do would be an actual reaction you could imagine yourself giving in response to that scenario.
This produces an extremely uneasy effect in which you cannot escape out of their terror-filled world because you feel, yourself, that you are in it.
There-in lies the key to this brilliant film. 
After a young, middle class couple moves into a suburban ’starter’ tract house, they become increasingly disturbed by a presence that may or may not be somehow demonic but is certainly most active in the middle of the night.
Especially when they sleep.
Or try to.
magic
