A rogue piece of patio furniture was swept off a Manhattan 12th-floor balcony by Saturday’s stormy weather and clocked a pedestrian in the head, police said.

The wooden lawn chair and its cushion were blown off the 12th floor of 15 Union Square West at about 2 p.m. and plummeted down to the sidewalk, hitting a 23-year-old woman in the head and damaging a parked car, officials said.

“She was passed out. We thought she was dead. It really hit her hard.” said Patrice Demay, 62, who witnessed the freak furniture fall from her stand at the nearby farmers market.

“All of a sudden, she started screaming. She woke up and she was in a panic,” Demay said. “She couldn’t move.”

The woman suffered a laceration to the head and was taken to Bellevue Hospital in stable condition.

The Department of Buildings was on the scene Saturday afternoon investigating the incident and securing the rest of the furniture from the building’s terrace, a spokesperson said.