You have to remind yourself to breathe.  It’s not that you’re literally stuck, in a coffin, with Ryan Reynolds for the 90 minutes that he’s “Buried.”  But this everybody’s-worst-nightmare thriller makes feel that you are.

“Buried” works on you that way.

A lean single-character exercise in limited space, limited movement and extreme close-ups, “Buried” is closer to this experience — kidnapped, entombed with just a cell phone and a Zippo lighter — than anyone would care to be.

In pitch blackness, a man wakes up. He’s bound and gagged. We only see his face when he’s able to get his lighter to work. And what he sees — the walls of a pine box, dirt occasionally dribbling in through cracks — is as chilling as it gets.

Where is he? How did he end up there? How can he get out?

Reynolds plays this fellow’s reactions right on the mark — confusion, panic, hysteria, rage. Whoever tossed him in there left a cell phone.  The lettering on it Arabic, but it’s his one hope of escape.

Filmmaker Rodrigo Cortes limits us to this man’s world — the box he’s in, and what he can experience-discover through that mysterious cell phone. Reynolds’ acting is mainly through the buried man’s increasingly frantic phone calls — getting people to pick up the phone, forcing the disembodied voice on the other end to take him seriously.

“I’m buried in a coffin” earns incredulous reactions from one and all,  starting with 911 operators and on up to the FBI. Reynolds makes us laugh at the frustrations we all experience dealing with a cell phones and operators, and he makes us believe that he believes this is a matter of life and death. He pleads, screams, weeps and bargains as if the stakes are real and the clock is running out.

Cortes (and writer Chris Sparling) make darkly humorous observations about the foibles of cell phones — crawling around in a box underground, trying to get reception. But “Buried” is also an ad for this vital tool of modern life — the ability to call anywhere and everywhere, leaving fearful good-byes, uploading photos and video, lighting the darkness. It’s a pity this phone doesn’t have a web browser. Maybe there’s a “What to do if you’re buried alive” website he could consult. Maybe watch that buried bit of “Kill Bill” for inspiration.

There have been other attempted acting exercises involving just a character and a phone (“Phone Booth,” “The Telephone”). But “Buried” success lies in its relentless claustrophobia.

The movie loses its ticking clock urgency at times. And it tips over into melodrama in its final third. But the performance and those who capture it on film put us in that box with Reynolds, make us feel his terror and leave us gasping and muttering at the screen — “Hey man. That lighter’s burning up our air!”

Cast: Ryan Reynolds

Director: Rodrigo Cortes

Running time: 1 hour 33 minutes

Industry rating: R for language and some violent content.