Carrie Fisher died from a little-known condition that may have been unrelated to the drugs in her system

Carrie Fisher died last year from what coroner's officials believe to be sleep apnea "and a combination of other factors," according to the results of her death inquiry.

Because Fisher's family did not authorize a full autopsy, officials were limited to drawing conclusions from an external exam, the results of which were released on June 16 and published in full by the Los Angeles Times on June 19. As a result, officials said they did not have enough evidence to "conclusively determine" the cause of Fisher's death.

Additional details from toxicology screenings taken when she arrived at the hospital showed Fisher had cocaine in her system, The Associated Press reported. However, officials believe she took it three days before the December 23 flight on which she got sick. Fisher died four days later, according to AP. Officials also found traces of heroin and MDMA in her system but couldn't say when she had taken those drugs.

Given the time frame, investigators could not say for sure what — if any — impact those drugs may have had on Fisher's death. Sleep apnea is therefore listed as the main contributing factor.

Sleep apnea is a chronic illness that involves pauses in breathing or shallow breaths while you sleep. It frequently goes undiagnosed, according to Nancy Foldvary-Schaefer, the Director of Cleveland Clinic’s Sleep Disorders Center.

"It's clear she used heroin, but it's not clear when," David Juurlink, a University of Toronto researcher specializing in pharmacotherapy and disease, told Business Insider. The report also showed signs of alcohol in her system, which he said "could have played a role too in terms of interfering with her breathing." Again, however, "the concentration isn't clear," said Juurlink.

Foldvary-Schaefer estimates that sleep apnea affects at least 9% of women and 24% of men. Many people are unaware they have it because it only occurs during sleep, so a family member or partner may be the first person to notice the signs. Left untreated, sleep apnea can increase the risk of high blood pressure, heart attack, stroke, obesity, and diabetes, according to the NIH. It can also raise the risk of or worsen heart failure, increase an individual's chances of work-related or driving accidents, and make arrhythmias (irregular heartbeats) more likely.

Fisher experienced a cardiac arrest on an airplane flight. As opposed to a heart attack, in which a blocked artery causes the heart to stop, a cardiac arrest involves a malfunction in the heart's functioning. She fell ill and lived for four days, but it could be that her sleep apnea, combined with possible drug use including alcohol, worsened the event and made it harder for her to fully recover.

In the opinion section at the back of her death inquiry report, Acting Chief Medical Examiner-Coroner Christopher Rogers wrote, "Based on the current information, the cause of death is 'Sleep apnea and other undetermined factors,' other conditions 'Artherosclerotic heart disease, drug use,' how injury occurred 'Multiple drug intake, significance not ascertained,' manner of death undetermined."