Sleep apnea is a common condition where breathing stops during sleep for a few seconds or minutes.
The report of forensic medicine referred to sleep apnea as a cause of death along with other factors, including heart disease and drug use.
"My mother has been struggling against drug addiction and mental illness throughout her life, and she eventually died because of it," Fisher's daughter said in comments published by People magazine after the forensic report.
"Throughout her work she has been vulnerable to the social stigma of such diseases."
But the forensic medical report excludes the hypothesis of suicide and says the cause of her death will be recorded as unspecified.
Fischer was on a tour to promote her "Princess Diaries" when she felt sick during a trip from London to Los Angeles on December 23.