In Adam Bock’s notes for “A Life,” a world premiere now at Playwrights Horizons, the author reports that both his parents died in quick succession -- seven weeks apart -- just a few years ago.

The “heartbreaking and incomprehensible” event has clearly informed the Obie Award winner’s disarming 85-minute drama, which features an unsettling performance by theater mainstay David Hyde Pierce, as an everyman gay New Yorker in his mid-50s.

Single (again) and with a caring social circle, Pierce’s Nate Martin, an ad agency proofreader, might well have been a stand-in for half the audience members at the recent performance I attended. He’s a guy like us. That’s relevant, given the startling direction “A Life” veers off in, halfway through.

“A Life” is staged upstairs at PH’s tiny Peter Jay Sharp Theater, and so when Pierce begins with a funny monologue about Nate’s interest in astrology, speaking from the orange sofa in his cozy apartment, we have the sense this is a one-on-one chat.

Nate turned to the stars decades earlier for help making sense of life after a chart reader promised wealth on the horizon … and then it materialized, in a way. His sense is that astrology may be as useful as any other roadmap for explaining the random events that comprise his life, or ours.

And then, a random event materializes. Stop reading if you want to avoid a big spoiler: In the middle of jotting a note on his to do list -- a ho-hum reminder to request a move at the office, away from a gum-chewing pod mate -- Nate grabs his arm and that’s it. It’s a heart attack.

Pierce pulls off the abrupt scene so effectively that for a moment I thought about calling 911. For the uncomfortable four or five minutes after, little happens: the lighting changes and we hear voices on the street, indicating the passage of time. All the while, Nate’s on the floor, slumped over.

Eventually, Nate’s friend Curtis (the relatable Brad Heberlee) gets help breaking into the apartment and discovers his friend’s body.

The rest of “A Life” depicts the banal mechanics of what happens when, say, you die in your apartment. You’ve thought about it, right? Other people going through your stuff? How everyone else’s life just … goes on?

The medical examiner’s team comes to remove Nate’s body. Curtis is there, trying to process his own shock, but the ME puts him off for a minute to answer her cellphone. It’s a call from her friend, who wants to talk about the new Fiat 500L she just bought: There will be no: “Hey, let me call you back.”

Later, two workers prepare Pierce’s body for burial, clipping his toenails, slathering moisturizer on his scrawny legs and finding the right shade of makeup for his colorless lips (“nude” works best). The women play music and chat about their dreary lives.

Laura Jellinek’s set for Nate’s apartment adjusts dramatically for the final scenes, which have Curtis and Nate’s sister (Lynne McCollough) giving eulogies at the funeral. Lighting and scenic design mesh to end the show with us believing we see Nate walking into his own coffin.

At the same time, we hear Nate speak in voiceover, talking about “the weight of the earth pressing down on the wood” of his casket. “A Life” is a cold, searingly honest and effective reality check. Every life includes a death.

“A Life,” through Nov. 27 at Playwrights Horizons Peter Jay Sharp Theater, 416 W. 42nd St. Tickets: $55-$99. Call 212-279-4200.

Follow Robert Kahn on Twitter@RobertKahn