Dia Dipasupil/Getty Images(NEW YORK) — Actress Emilia Clarke, better known as Daenerys Targaryen on the hit HBO show Game of Thrones, revealed that she had survived two brain aneurysms while filming the show’s early seasons in an essay published in The New Yorker on Thursday.

She said that in 2011, after wrapping up the first season of the show, she had been working out at the gym when she suddenly developed a headache. She said it was “as though an elastic band were squeezing my brain.”

Although Clarke tried ignoring it, she said that it persisted and that she eventually had to be rushed to a hospital, where doctors diagnosed her with two aneurysms, one of which burst open. Doctors were able to treat that one with minimally invasive surgery.

The other one, however, became a problem in 2013. During a routine brain scan monitoring the aneurysm, she said she discovered that it had doubled in size. She thought that she would be undergoing a procedure that was less invasive than the first but in the middle of it, the aneurysm burst and Clarke had to undergo open-brain surgery, which she was fortunate enough to recover from.

“In my years since my second surgery I have healed beyond my most unreasonable hopes,” she said.

Clarke’s story stands out not only because of her fame but also because her experiences with brain aneurysms are somewhat rare. How so? Here’s what you should know about brain aneurysms:

Brain aneurysms are relatively common, but few actually cause serious problems

A brain aneurysm occurs when a blood vessel in the brain has a weak spot that causes it to bulge and fill with blood. There are three types of aneurysms, with each developing for different reasons: some develop at the branch points of the blood vessels, others because of abnormalities in the blood vessel walls and still others because of an infection.

Most don’t ever cause symptoms. But when the blood vessel grows in size, the aneurysm can compress nerves and cause stroke-like symptoms. Other symptoms include vision changes, numbness, or weakness.

The aneurysm becomes a bigger problem when the blood vessel bursts — this causes bleeding in the brain known as a subarachnoid hemorrhage, which is what Clarke experienced. These usually happen suddenly and cause terrible headaches.

Like many others who’ve described these headaches, Clarke said hers was “shooting, stabbing, constricting” and that “at some level, I knew what was happening: my brain was damaged.”

Bleeding in the brain can also cause nausea, vomiting, neck stiffness, light sensitivity, seizures, difficulty speaking or loss of conscious. It can also result in stroke or even death. In fact, in 2015, WABC-TV reporter Lisa Colagrossi died of a brain aneurysm at age 49.

About 4 percent of the population has a brain aneurysm at some time in their life, but far less have aneurysms that burst — about 30,000 Americans each year. Brain aneurysms typically occur between the ages of 30 and 60 and are more common among women. About 20 to 30 percent of people who have aneurysms also end up with more than one.

Personal habits and hereditary diseases can increase risk for aneurysms

Some risk factors that can increase a person’s chance of developing a brain aneurysm include smoking, alcohol use, recreational drug use and high blood pressure. A variety of inherited diseases can raise the risk, too, including polycystic kidney disease, fibromuscular dysplasia, aortic coarctation, arteriovenous malformations and a connective tissue disease called Ehlers-Danlos syndrome. Even having a family history of brain aneurysms can increase the risk of forming a brain aneurysm.

There are two main treatments for aneurysms that cause symptoms

Aneurysms are diagnosed with brain imaging tests, such as an MRI or CT scan, which is commonly referred to as a CAT scan. Sometimes, aneurysms are accidentally picked up on scans ordered for other reasons. When an aneurysm is small or does not cause symptoms, repeat imaging is recommended every year to make sure the aneurysm isn’t growing.

There are two main treatments for aneurysms that are either causing symptoms or large in size. The more common treatment is called coiling, and it involves a doctor guiding a catheter through the groin up to the brain, where they release metal coils that plug up the aneurysm. This is the preferred method because it is less invasive. The other treatment, called clipping, requires open-brain surgery and involves closing the aneurysm with a metal clip.

The risk of death is high if an aneurysm bleeds

Many people with aneurysms live a long, full life and never even know it was there. If an aneurysm is discovered before symptoms, the treatments are effective. However, once an aneurysm bursts, the prognosis is grave. Twenty-five percent of people with a ruptured aneurysm don’t survive the first 24 hours after it happens, while another 25 percent die within the first six months of the rupture. Those who survive, meanwhile, are likely to suffer lifelong, permanent neurological damage.

Most people don’t have to worry about having a brain aneurysm

There is no formal recommendation for screening for brain aneurysms because of the low risk an aneurysm in the brain will burst, the risks associated with treatment and the anxiety that finding an aneurysm can provoke. That said, people with a first-degree relative or medical condition known to increase risk for brain aneurysms can consider getting screened.

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