Check out this wonderful, unforgettable spanish movie on that theme, much better than any plot summary could suggest (and also I don't want to give spoilers) :

Check out this wonderful, unforgettable spanish movie on that theme, much better than any plot summary could suggest (and also I don't want to give spoilers) : The Uninvited Guest (El habitante incierto) https://www.imdb.com/title/tt0436374/ https://www.imdb.com/title/tt0436374/ Taking the theme to a fantastic extreme is the amazing french miniseries Beyond the Walls (Au-delà des murs), which has a whole bizarre world secretly living in your house. https://www.imdb.com/title/tt4999820/ https://www.imdb.com/title/tt4999820/