Square Peg in a Black Hole (1970)

Alma, a theater assistant in her mid-30s, goes to the bathroom during rehearsals. In the dead quiet of the bathroom stall, she succumbs to a full-blown existential crisis, only to be interrupted in the next instant by an explosion in the neighboring cubicle. Alma investigates and finds that a black hole has formed in the toilet bowl. Entranced by the pull of the swirling void, she reaches inside and is transported into several vignettes about the meaning of life.