Other reviews have noted similarities to (and the film actually name-checks) The Twilight Zone, and it does so as more than simply a code for "something freaky's going on here." The film's plot absolutely feels like something out of a Richard Matheson episode. And of course, I can't even reference which Matheson episodes came to mind as I watched this, because spoilers.
The one thing this film has over a Twilight Zone episode is the feeling the film's resolution leaves me with, which I can only describe as the same feeling described by Bruce Sterling in his oft discussed and debated definition of "slipstream," namely "...a kind of writing which simply makes you feel very strange; the way that living in the twentieth century makes you feel, if you are a person of a certain sensibility." If slipstream is that form which is, as it's said, "some degree of the surreal, the not-entirely-real, or the markedly anti-real" then I'd definitely call this a slipstream film.