A Fox News Channel source said Cindy Anthony made the statement during an interview for the "Dr. Phil Show" that will air Monday, WFOL-TV, Orlando, Fla. reported Thursday.
Cindy Anthony told Dr. Phil McGraw her daughter, Casey, suffered what appeared to be a gran mal seizure in 2005 and may have suffered another one in 2008 while Caylee was dying, the source said.
Gran mal seizures involve a loss of consciousness and violent muscle contractions.
They are most often caused by epilepsy but can be triggered by other health problems such as low blood pressure or a stroke.
Cindy Anthony pointed to the seizures as evidence Casey had a mental health condition that may have incapacitated her while Caylee was drowning in the family swimming pool, the report said.
Casey was acquitted July 5 of killing Caylee but found guilty of lying to police during the investigation of Caylee's death.