I saw this just yesterday without knowing absolutely anything about it (no trailer, no reviews, no synopsis) and it was nerve-wracking. Half the film is building up to a long sequence that occupies the other half of the film where the lead is in the exact same position as us as far as knowing what the fuck is going on. It's very low budget filmmaking and some of the acting could maybe have been better but writer-director-star Ana Asensio nails this: short, slow-burning and creepy, just the way I like 'em.