Jennifer Aniston is enjoying the happiest moments of her life as she prepares to wed her fiance Justin Theroux, but at the same time the actress is suffering darkness in another part of her personal life.

The 43-year-old former "Friends" star is worried that her mother, 76-year-old Nancy Dow, is suffering from the early stages of Alzheimer's, according to a new report from The National Enquirer.

"It's heartbreaking. Her mom's deterioration has been shocking, and Jen just wants to see her well again," a source said. "Jennifer can't bear to think of her mother having such a terrible, incurable disease."

Dow has become increasingly confused about her surroundings and may be experiencing some dementia, the report said. Aniston's mother also fractured her shoulder on Election Day when she took an unfortunate fall as she was entering her polling place to vote.

Aniston has watched her mother as she has slowly begun losing her memory, and the family has been meeting with a medical team to determine what their treatment options might be.

"The doctors are doing more tests and there's also a very real concern she may be in the early stages of Alzheimer's," the insider said. "She slips into periods of confusion, at times doesn't recognize people and her short-term memory appears to be damaged. It's sad. It's tough for the whole family."

Aniston and her mother have had quite the rocky relationship over the years. The women became estranged after Dow wrote a book about Aniston and the actress felt betrayed, so much so that she did not even invite her mother to her wedding ceremony to Brad Pitt in 2000.

Tags: Jennifer Aniston Justin Theroux