New York (CNN) -- Kerry Kennedy, the daughter of the late Robert F. Kennedy and ex-wife of New York Gov. Andrew Cuomo, said a partial seizure is the cause of a Friday morning car crash. At a press conference on Tuesday, Kennedy also said the seizure might have been from a previous injury she suffered on the right side of her brain.
Kennedy, 52, was found by state police behind the wheel of her damaged Lexus SUV. A New York State Police press release said the SUV collided with a tractor-trailer.
At a hearing on Tuesday in district court in North Castle, New York, Kennedy pleaded not guilty to charges of driving while impaired. The judge released her under her own recognizance.
At the press conference after the hearing, Kennedy said she told the officer who arrived at the scene: "It is theoretically possible that I might have taken an Ambien rather than a thyroid pill" earlier that morning. Kennedy said she remembers nothing of her alleged erratic driving, from getting on the highway until the officer stopped her at a traffic light.
"A subsequent investigation found Kennedy to be operating the motor vehicle while her ability was impaired by drugs," police said in announcing the charge against her on Friday.
At Tuesday's press conference, Kennedy said she went to Northern Westchester Hospital, where she was tested for recreational drugs, prescription drugs and alcohol. Kennedy said the results came up negative.
She did not say whether her thyroid medication showed up in the test results.
Determined to understand her medical condition, Kennedy said she visited Mount Sinai Medical Center, where she underwent "a full battery of neurological testing."
"Doctors believe that the crash was caused not by a sleeping aid, but by a complex partial seizure," Kennedy said. She did not take questions.
This is the second time this year that a high-profile person suffered a seizure that resulted in a car accident. In June, U.S. Commerce Secretary John Bryson, who has since resigned, was involved in two car crashes in the Los Angeles area before being found unconscious in his car, police said. Bryson was not charged.