A telephone call from a friend alerted the police that the woman had taken a sleep medication and had left her home in the town of Hamilton in her car, police chief Dave Litton told the Fairfax media group on Wednesday.
The woman, who suffers from a sleep disorder and in a similar incident 10 months ago, drove several kilometers while she was asleep, said she did not remember anything about her journey after she was found in front of her old beach house in Mount Maunganui.
"Her cousin found her sleeping, collapsed over the steering wheel," said Litton.
Authorities have requested an urgent court order prohibiting her from driving, pending a medical examination, he said.
Police followed the car after locating it using the woman's cell phone, which she used to send several text messages during the five or so hours it took her to drive about 300 km.
"While her being found safe and well is a relief for everyone involved, the potential for tragedy was huge and we're urging people suffering medical conditions to be open and honest with their doctors and seek advice on the medication they are prescribed," Litton said.