Sleep Tight (original title Mientras duermes) is a masterfully unsettling Spanish thriller from 2011 that crawls under your skin and stays there. Directed by Jaume Balagueró, the film presents a chilling character study of César, an apartment building superintendent portrayed with unnerving calm by Luis Tosar. His performance is the film's terrifying anchor—a man whose mundane exterior masks a profound need to inflict misery, finding his latest target in Clara, the seemingly cheerful occupant of apartment 5B.

The plot unfolds with methodical, suspenseful precision. Balagueró's direction is clinical and intimate, turning the familiar setting of an apartment building into a claustrophobic prison. The film is less about graphic violence and more about psychological violation, exploring the horror of having one's safest space invaded. The cat-and-mouse dynamic builds unbearable tension as César's manipulations become increasingly invasive.

Viewers should watch Sleep Tight for its exceptional execution of psychological dread. It's a thriller that prioritizes character and atmosphere over cheap scares, resulting in a far more lasting sense of unease. The film's strength lies in its plausibility and the superb, understated performance from Tosar, who makes monstrous behavior feel disturbingly mundane. For fans of international cinema and sophisticated, character-driven thrillers, this is a must-watch experience that demonstrates the power of quiet, relentless horror.