By Dan Whitcomb

LOS ANGELES (Reuters) - Prosecutors declined to file charges against former U.S. Commerce Secretary John Bryson on Tuesday over his role in two car crashes on the same day in June after blood tests showed he had only low levels of a sleep aid in his system at the time.

Bryson was found unconscious behind the wheel of his Lexus on June 9 after he crashed into one car twice, left the scene of the accident and later collided with another vehicle, according to authorities.

Bryson had the prescription drug Ambien in his system at the time of the incident and doctors concluded he was confused after suffering a seizure, a Los Angeles County prosecutor said in a document explaining the decision.

The 68-year-old former energy company executive announced his resignation less than two weeks after the crashes, citing a seizure he and Commerce Department officials said he suffered on that day.

Police said they had asked prosecutors to file hit and run charges against Bryson.

"Based on doctors' opinions there is insufficient evidence to show knowing failure to provide personal information for hit and run," Deputy District Attorney Deborah Kass wrote in the document.

"Further, based on blood test and medical condition there is insufficient evidence to prove driving under the influence," Kass wrote.

Bryson, who had run the Commerce department for less than a year at the time of the accidents, had been alone in his car and authorities had initially said there was no indication alcohol or drugs played a role in the collisions.

He was treated at the scene, regained consciousness and was admitted to a local hospital. Passengers in the other cars had no major injuries.

Bryson is a former chief executive of Edison International, a public utility holding company headquartered in Rosemead, California. He had served as Obama's secretary of commerce since October 2011.

(Editing by Cynthia Johnston, Cynthia Osterman and Andrew Hay)