The 26-year-old hotel heiress was sent home shortly after 2 a.m. fitted with an electronic monitoring bracelet. She had spent five days at the Century Regional Detention Facility in suburban Los Angeles for violating probation in an alcohol-related reckless driving case.
"I can't specifically talk about the medical situation other than to say that, yes, it played a part in this," said sheriff's spokesman Steve Whitmore.
Hilton had been sentenced to 45 days behind bars, but had been expected to serve 23 days because of state rules allowing shorter sentences for good behavior.
Whitmore said that under the new agreement, Hilton would be confined to her home for 40 days.
"Because she has agreed to this through her attorney, her sentence is now back up to the 45 days. She has served already five days so that's 40 days," he explained.
Hilton checked into the Century Regional Detention Facility just after 11:30 p.m. Sunday. She had surrendered to authorities with little fanfare after a surprise appearance at the MTV Movie Awards, where she worked the red carpet in a strapless designer gown.
"I am trying to be strong right now," she told reporters at the time. "I'm ready to face my sentence. Even though this is a really hard time, I have my family, my friends and my fans to support me, and that's really helpful."
Hilton was housed in the "special needs" unit of the 13-year-old jail, separate from most of its 2,200 inmates. The unit contains 12 two-person cells reserved for police officers, public officials, celebrities and other high-profile inmates. She didn't have a cellmate.
After she checked in Sunday, Whitmore said Hilton's demeanor was helpful.
"She was focused; she was cooperative," he said.
Hilton's lawyer, Richard A. Hutton, said Monday after his client's first night in jail that she was doing well under the circumstances.
"She's using this time to reflect on her life, to see what she can do to make the world better and hopefully, in my opinion, to change the attitudes that exist about her among many people," Hutton said after visiting Hilton.
The 13-year-old jail, a two-story concrete building next to train tracks and beneath a bustling freeway, has been an all-female facility since March 2006. It's located in an industrial area about 12 miles southeast of downtown Los Angeles.
When she was sentenced May 4, Superior Court Judge Michael T. Sauer ruled that she would not be allowed any work release, furloughs or use of an alternative jail or electronic monitoring in lieu of jail.
Officers arrested Hilton in Hollywood on Sept. 7. In January, she pleaded no contest to the reckless-driving charge and was sentenced to 36 months' probation, alcohol education and $1,500 in fines.
She was pulled over by California Highway Patrol on Jan. 15. Officers informed Hilton she was driving on a suspended license and she signed a document acknowledging she was not to drive. She then was pulled over by sheriff's deputies on Feb. 27, at which time she was charged with violating probation.