The dementia drama is on something of an upswing, and recently actors like Anthony Hopkins, Bruce Dern and Javier Bardem have joined the growing ranks of performers eager to portray a fragmenting mind.

Of these, Lance Henriksen’s work in “Falling” might be the most brutally demanding, and the hardest to watch. As the foul-tempered, bigoted Willis, the actor is a weeping wound of intolerance and invective. Fully committing to dialogue rarely heard outside of scabrous comedies, Henriksen is the incendiary heart of a movie that ultimately proves more involving — and rather more complicated — than we expect.

We meet Willis during a tantrum on an airplane. His middle-aged son, John (Viggo Mortensen, in his writing and directing debut) is bringing him to Los Angeles to house-hunt. Willis, no longer able to manage his beloved farm in upstate New York, has reluctantly agreed to move closer to John and John’s sister, Sarah (Laura Linney). In the meantime, he will stay with John and his husband, Eric (Terry Chen), and their young daughter (Gabby Velis). Brace for the homophobic slurs.

Extensive flashbacks reveal that Willis has always had a mean streak (“I’m sorry I brought you into this world, so you could die,” are some of his earliest words to the infant John), but illness and the early stages of senility have made him monstrous. Somehow, though, Henriksen lets us see the loneliness and fear that gnaw at the edges of Willis’s anger — and help explain why John responds to his father’s abuse with such calm resignation. The film, though, is not without its comic moments: I’ll go a long way to see David Cronenberg play a proctologist.

A small movie with outsized philosophical ambitions, “Falling” doesn’t go down easily. The nuanced performance of the Icelandic actor Sverrir Gudnason, who plays the younger Willis, is crucial, exposing the volatility and subdued menace that has alienated two wives and caused untold damage to his children. Some scenes scrape your senses like sandpaper, while others are so tender they’re almost destabilizing. Together, they shape a picture that’s tragically specific, yet more comfortable with mystery than some viewers might prefer.

Though not entirely autobiographical, “Falling” is informed by Mortensen’s memories of caring for several family members stricken by dementia. The result is a movie keenly aware of the effort involved in reconciling the parent we have with the one we might have wished for.

Falling
Rated R for sexism, racism, homophobia and terrible table manners. Running time: 1 hour 52 minutes. Rent or buy on Google Play, Vudu and other streaming platforms and pay TV operators.