Sorry for the bad info, but I seem to remember watching an older movie (60's-70's?) in which a woman finds out there is some sort of creature nesting in her apartment building (either wall or closet.) It kind of happens suddenly at theend that they show this weird thing and you're like WAIT WHAT. Thanks!!
Sounds a bit like an episode from Nigel Kneale's short-lived series, Beasts called "BABY" (https://celluloidwickerman.com/2014/11/27/hysteria-and-curses-in-nigel-kneales-baby-beasts-1976/ (https://celluloidwickerman.com/2014/11/27/hysteria-and-curses-in-nigel-kneales-baby-beasts-1976/)
This makes me think of the episode "inside the closet" from the "Tales from the Darkside" series. Its my favorite episode from this series, starring the late great Fritz Weaver.
although it doesn't seem like either of those they both look f**kin amazing!!!! thabks :)
i wonder if it might be this?
http://www.imdb.com/title/tt0082804/?ref_=nv_sr_1 (http://www.imdb.com/title/tt0082804/?ref_=nv_sr_1)