Someone called 911 from the golfer's Orlando-area mansion about 2:35 a.m.
Barbro Holmberg was taken by ambulance to Health Central Hospital, where she was stable later Tuesday, hospital spokesman Dan Yates said. He said her condition was not serious, but he could not be more specific because of privacy laws.
Ms. Holmberg, who arrived in the U.S. a few days ago, lives in Sweden and is the mother of Woods' wife, Elin.
Health Central is the same hospital where Woods was treated after he crashed his sport utility vehicle outside his home last month.
Yates said Ms. Holmberg was in a private room and the family has hired additional security to keep the media away. He said family members have visited her, but he would say who.
"She's in a wing that helps protect her privacy," Yates said.
Media attention has been focused on the world's No. 1 golfer since he hit a hydrant and a tree around 2:25 a.m. on the Friday after Thanksgiving.
The Florida Highway Patrol last week cited Woods for careless driving and fined him $164.
The accident and Woods' refusal to answer questions about it fueled speculation about a possible dispute between him and Elin.
Just days before the crash, a National Enquirer story alleged Woods had been seeing a New York nightclub hostess, Rachel Uchitel, who has denied it. After the crash, Us Weekly reported that a Los Angeles cocktail waitress named Jaimee Grubbs claims she had a 31-month affair with Woods.
Last week, Woods issued a statement saying he had let his family down with unspecified "transgressions" that he regrets with "all of my heart." He did not elaborate.
A police report on the crash released Monday showed that a Florida trooper who suspected Woods was driving under the influence sought a subpoena for the golfer's blood results from the hospital he was taken to after the crash, but prosecutors rejected the petition for insufficient information.
A witness, who wasn't identified in the report, told trooper Joshua Evans that Woods had been drinking alcohol earlier. The same witness also said Woods had been prescribed two drugs, Ambien and Vicodin.
The report did not say who the witness was but added it was the same person who pulled Woods from the vehicle after the accident. Woods' wife, Elin, has told police that she used a golf club to smash the back windows of the Cadillac Escalade to help her husband out. His injuries were minor.
The sister of a neighbor who called 911 after the crash told troopers that Holmberg and Woods' mother, were also at the scene, but the AP has not been able to confirm that.
Eva Malmborg, a spokeswoman for Ms. Holmberg, said she could not comment on Tuesday's reports.
Malmborg confirmed that Ms. Holmberg had taken a week's leave from her job as Gavleborg County governor in central-east Sweden, but said she did not know where Ms. Holmberg had gone.
There was no sign of emergency workers later Tuesday morning at the Woods' gated community, where luxury SUVs and cars drove in and out as a few reporters and television news trucks milled around outside.