Christian Bale, the hale, muscular Welsh actor we remember from “American Psycho” and “Shaft,” is an emaciated sliver of his former self in “The Machinist.”

As Trevor Reznik, a heavy-machine operator whose mind and body seem to be fleeing him with alarming alacrity, Bale looks like one of those pathetic survivors led by the fingertips from Auschwitz. Stretching in the pasty morning light to the creeped-out delight of his hooker girlfriend (Jennifer Jason Leigh), exposing a near-fleshless skeleton of sinew and bone, Reznik cuts a frighteningly gaunt figure; something is literally consuming him from the inside out.

What that “something” is proves to be the driving mystery behind “The Machinist,” a deliciously layered psychological thriller made all the more intriguing by the fact that Reznik is just as baffled by his weight loss as we are. Is it a disease? Male anorexia? Subconscious penance? Unable to string together more than a few minutes of sleep, Reznik compulsively scrubs his bathroom grout and imagines conspiracies at work, especially with the arrival of a bald, boisterous arc welder (John Sharian) who slips in and out of the shop without anyone (except Reznik) noting his presence.

Despite a somewhat heavy-handed fondness for literary allusions — we see Reznik pick up a copy of Dostoyevsky's “The Idiot”; later, he passes a carnival ride labeled “Crime and Punishment” — director Brad Anderson masterfully metes out the movie's secrets. Shot in stark, washed-out grays in a wasted urban sprawl that might double for hell itself, the film is keenly matched in form and function, much like Christopher Nolan's “Memento” and Darren Aronofsky's “Requiem for a Dream.” Scott Kosar's script is a treat (this is the same guy who penned the miserable “Chainsaw Massacre” remake?), and the spooky B-movie scoring, by composer Roque Banos (“Sexy Beast”), haunts the film's margins with chilling ghoulishness.

Above all else, Bale — who will star in the title role of Nolan's “Batman Begins” next summer — makes “The Machinist” click. Forget, for a moment, the stunt weight loss (60 pounds, by the actor's account) and watch the performance. Bale fully comprehends this character; he is morose when he needs to be, puzzled and desperate and then — in a series of surreal coffee shop scenes with actress Aitana Sanchez-Gijon — oddly, artificially chipper. It all points, possibly, to the emergence of a young Jack Nicholson. About that weight loss: It makes Tom Hanks' transformation in “Cast Away” look like a poseur low-cal Subway commercial. You could call it gutsy, but it could be more than that — a leap forward in actorly daring that takes gutsiness to masochistic extremes.