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/
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.