Carrie Fisher died from sleep apnea, among other factors, according to a statement from the Los Angeles County Coroner’s Office. Although she was open about her struggle with drugs and there were signs of use, the medical examiner could not conclude whether they played a role in her death last December.

Therefore, her manner of death will be listed as undetermined, the Associated Press reported.

Read: What Is Yohimbe: Sleep Apnea Patients May Find Relief In All-Natural Aphrodisiac

It came as no surprise to her family that LSD and other drugs she said she used may have played a role in her death. “I am not shocked that part of her health was affected by drugs,” her brother, Todd Fisher, told The Guardian. “If you want to know what killed her, it’s all of it.”

One of the more surprising factors is sleep apnea. Here’s what you need to know about the serious sleep disorder that played a role in the death of the 60-year-old Star Wars actress.

What is Sleep Apnea?

It’s an often undiagnosed disorder that causes you to start and stop breathing, or have shallow breaths while you sleep, according to the National Institutes of Health. The short or stopped breaths can happen 30 times or more during an hour. There are three main types of the disorder: obstructive sleep apnea, central sleep apnea, and complex sleep apnea syndrome. The most common form of the condition, obstructive sleep apnea, causes the airway to relax or become blocked during sleep. It can affect anyone, but it’s most common in people who are overweight, male, or have a family history of the disorder.

Read: Sleep Update 2017: Dietary Supplement From African Tree Bark May Treat Obstructive Sleep Apnea

Signs And Symptoms

The signs vary depending on the type of sleep apnea a person has. One of the most distinct signs of obstructive sleep apnea is loud snoring or choking, which signals that normal breathing is starting again. Other common signs include awakening with a dry mouth or sore throat, morning headache, insomnia, hypersomnia, attention problems, and irritability. It’s a common problem that affects more than 18 million Americans, according to the National Sleep Foundation. If left untreated, it can lead to other serious health issues.

“What you die of is not the sleep apnea,” John Bouzis, a dentist who works with sleep specialists, told The Washington Post. “You die of the cardiovascular disease. You die of the stroke. You die of the pulmonary problems … Sleep apnea is a time bomb.”

See also: Is Weakened Heart Health Linked To Years Of Drug Abuse? Carrie Fisher's Heart Attack Death Raises Questions On Effects

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