Truly terrifying movie?

Im trying to find a movie that is horrifying. Like cant-sleep, paranoid movie. I don't watch slasher movies like "scream" or "Halloween". I don't care much for "nightmare on elm street". I dont want "the exorcist" or "psycho" I understand that it all depends on perspective,but i just want to watch a scary movie. I've already watched "cannibal holocaust" and it did nothing but make me gag. Im not really intrested in ghost movies. I want something disturbing and unnatural like "silent hill" or "the grudge" if you understand what im saying,help me out.