18 Jul 2012 03:25 PM EST

-by Anthony Bell, Contributing Writer; Image: Kerry Kennedy (Image Source: AP)

Kerry Kennedy pleaded not guilty to driving under the influence, claiming that a seizure was the cause of her car accident on July 13.

Kennedy, ex-wife of New York Governor Andrew Cuomo and daughter of Robert F. Kennedy, was arrested the morning of Friday the 13th when she was found behind the wheel of her disabled Lexus SUV at around 8 a.m. after hitting a tractor-trailer in North Castle, N.Y.

Police say Kennedy, 52, was seen driving erratically on Interstate 684 in the early morning hours before hitting the truck. They add that her speech was slurred and she failed multiple sobriety tests.

Now, Kennedy says she may have mistakenly told cops she took the sleeping pill Ambien that day instead of thyroid medication, according to TMZ, adding that tests showed “no alcohol, recreational drugs or prescription medication in my system.” She also received neurological testing after the crash, with an MRI revealing “an area of hyper density" in her brain, which she believes is from past head injury.

“I have never had a history of drug and alcohol abuse,” Kennedy explained to Judge Elyse Lazansky last night in court in North Castle, according to the New York Daily News. “I was asked if I had taken any medications. I volunteered that I take two prescriptions—one that I take every day for a thyroid condition and another, Ambien, which I take on average about once a month to help me sleep.”

“I told the officer that it was theoretically possible that I had mistakenly taken an Ambien instead of the thyroid pill early that morning,” she claimed. “I remember getting into the highway and then I have no memory until I was stopped at the traffic light. A police officer was at my door... Shortly after I was stopped by the police officer my mind began to clear up.”

She told the judge that she felt “confused and erratic” and misspoke to the officer of her possible pill blunder. Blood and urine tests for substances have not been completed, however, according to Lazansky.