A 911 dispatcher was caught on tape laughing about a call for a Brooklyn stabbing — then passing along bad information to cops that allowed the victim’s body to rot for days in a basement apartment.

The woman found it hysterical that a mental patient — whose shrink had just called in the potential murder — wasn’t sure whether he had imagined stabbing his girlfriend or if it really happened.

“This man said that he had a dream that — I can’t even talk right now,” the woman chortles on a recording obtained by The Post.

But the dream turned out to be real, cops say.

Ronald Friedfertig was arrested Wednesday for allegedly stabbing Yvonne Geffner to death in their Midwood apartment.

A note left behind said, “She was casting spells on me.”

The shrink made the 911 call on May 30, but Geffner’s body wasn’t found until four days later, when neighbors reported a stench.

“[The call center] got a call for a person possibly stabbed inside a home,” a law-enforcement source said. “The door should have been taken down.”

But cops weren’t told that no one had seen the woman in a week — or that the man’s psychiatrist made the call — so they just knocked and left when no one answered, a source said.

NYPD brass are furious. “They are pissed, and they’re trying to get to the bottom of it,” a source said.

Friedfertig initially told his brother, Menacham, he had a vision that he stabbed Geffner.

Menacham then told the shrink, Noam Koenigsberg.

“He’s not sure if it was real or if it was a dream, but no one has been able to reach [the victim] since,” the doctor told one dutiful 911 operator, Vera McFarland.

McFarland accurately and professionally took down the information and said, “I just hope that it’s not true, but you never know.”

She passed the information to the childish dispatcher, who could barely contain herself, saying the report was “crazy.”

She told a cop no assault had occurred and even mixed up the victim and suspect, mistakenly telling police a hospitalized man wanted his home checked because he dreamed he was attacked there.

By the time cops busted down the door, Friedfertig was already in a mental hospital after throwing himself in front of a Q train.

He’s awaiting arraignment on murder charges as he recovers at Kings County Hospital Center.

An NYPD spokesperson said that the allegations against the dispatcher are being investigated.

Additional reporting by Dan MacLeod