A 30-year-old was having lunch when she collapsed. She'd had a cardiac arrest.

A 30-year-old woman was left fighting for her life after her heart suddenly stopped beating.

In October 2015, Katrysha Gellis was at work when she started to feel unwell. Almost immediately she collapsed and her heart stopped working. She'd had a sudden cardiac arrest.

Gellis told BBC "Heath Check": "My colleagues were very quick to call 911 and then start chest compressions.

"They started pressing on my chest and that pushed the blood around my body and kept oxygen going to my brain so it was essentially keeping me alive."

Shortly afterwards, a team of firefighters picked up the 911 call and arrived on site. They used an automated external defibrillator to restart her heart.

Gellis had just turned 30 and was a healthy person with no known heart conditions in the family. She later found out that an arrhythmia — an abnormal heart rhythm — had caused her heart to stop beating, but doctors couldn't find an official cause.

According to Sudden Cardiac Arrest Foundation, one in 10 survive sudden cardiac arrest and it can affect people of any age who may seem perfectly healthy.

When bystanders give immediate CPR, survival rates of SCA victims can double or triple, the foundation states.

Following her cardiac arrest, Gellis was fitted with a device called an implantable cardioverter defibrillator that would shock her heart back into the correct rhythm if needed.

Doctors told her that although it would be unlikely for her to experience another cardiac arrest, the ICD was there to protect her should it happen again, she told Insider.

Gellis had another cardiac arrest years later

Over six years later, in January 2022, Gellis was at home when she had another arrhythmia and collapsed. The ICD shocked her heart into restarting while her husband called 911. She'd had another cardiac arrest.

Unlike with her first cardiac arrest, Gellis had vivid memories of the whole event, leaving her feeling traumatized.

She told Insider: "I think like any trauma, it just takes some time to heal and to process." With the help of a therapist, she started to process the emotions and a year on she feels like she's in a strong place.

Gellis said that experiencing cardiac arrest — whether it be yourself or witnessing as a bystander — can be a traumatic experience and there's a gap in care for survivors as well as their families and bystanders.

The symptoms of a cardiac arrest and a heart attack are different

After Gellis had her first cardiac arrest, she became a certified CPR instructor and has shared her story to raise awareness. She said that it is important to know the signs of a cardiac arrest, which is different from a heart attack.

According to the Sudden Cardiac Arrest Foundation, when a person is having a heart attack they are awake and their heart will continue to beat.

Heart attacks happen when blood supply to the heart is reduced or blocked, and can cause discomfort in the center of the chest that lasts more than a few minutes or goes away and comes back, the foundation says.

A cardiac arrest is when the heart stops beating altogether.

The foundation says that with a sudden cardiac arrest, victims won't be responsive or breathing normally and will need CPR and to be treated with an AED.

Gellis said: "If they're unconscious and not breathing normally, then you call, push, and shock." This refers to calling 911 and requesting an AED, pushing on the chest and starting CPR, and shocking them with an AED.

She said: "Anybody, no matter who you are, can empower themselves with knowledge to be confident to react."

CPR classes can help people feel comfortable in emergency situations, rather than getting overwhelmed, Gellis said. She added that people don't need qualifications to perform CPR and use an AED in an emergency situation.