'I was in the car when I looked at my baby in the rear-view mirror. I'll never forget what I saw.'

It was 11pm at night on Cavill's 29th birthday.

Driving down a (thankfully) quiet highway, Cavill's partner Adam suddenly slammed on the brakes, yanking their car across three lanes to the side of the road. Terrified, she looked in the rear-vision mirror to see her one-year-old daughter Emmy convulsing in the backseat.

"We had no idea what was going on," Cavill told Mamamia. "I just remember needing to get in the back as quickly as possible, even though I didn't know what I would do when I got there.

"To look back at her, and her little arms and legs were stretched out, and her head was back. I will never forget the visuals," Cavill added.

Watch: What to do if someone is having a seizure. Post continues below.

The next 17 minutes as they waited for an ambulance to arrive felt like a lifetime for the parents. Emmy was unresponsive, and Cavill thought she had stopped breathing.

"My husband was trying to breathe into her mouth and give her CPR. But we had no first-aid training."

Unsure whether to move her baby, a desperate Cavill directed her questions to the emergency dispatcher. Is she going to have brain damage? Is she going to die? She went through every nightmare scenario, her panic increasing.

Though the dispatcher tried to keep her calm, nothing could quell the "feeling of absolute helplessness", said Cavill.

Then.

Sirens blared in the distance, flashes of blue and red lighting up the highway.

"'Oh, they're here! They're here!" Cavill said down the phone. But her relief dissipated at the dispatcher's next words.

"Oh, honey, I'm so sorry. That's not for you."

Recalling the moment, Cavill still gets goosebumps.

"I remember watching the ambulance go past and thinking, 'But we need help right now. Why can't that be for me?'"

It took another eight minutes for their paramedics to arrive. Assessing the situation and realising Emmy had a fever, they suspected she had suffered a febrile seizure — a convulsion in a child that may be caused by a spike in body temperature.

"The way that he explained it to me was, it's your body needing a hard reset, like with an old PlayStation or an old laptop," Cavill said. "You force a restart and everything crashes, and then it all comes back.

"So they've gotten really sick, really suddenly, and their fever's gotten so high that their little bodies malfunction. It's like a forced reset. That's why they can be a bit unresponsive afterwards, because everything's starting to work again."

Emmy suffered from febrile seizures. Image: Supplied

Once a child has had one febrile seizure, their chances of having another one increases — a scary thing for parents. 

"I remember hearing them say that on the side of the road, and just being like, 'I can't go through this again.'"

Over the next 18 months, however, Emmy went on to have seven more seizures. 

"She had one at kindergarten. She had one at each of her grandparents' houses. She had one in the bath. Whenever she would get sick, she would have this rapid fever, and then she would have a seizure."

Cavill's anxiety spiralled out of control as a result. Just weeks after the initial incident, the mother-of-one woke up feeling as though she was in a fast-braking car. As the months progressed and more seizures occurred, the scenarios in her head got worse.

"I started worrying about things that I had never, ever worried about before," she said. "I started worrying about her choking, I started worrying about her drowning. It was controlling me. Every time she would feel the tiniest bit warm, I would start panicking."

During this time, Emmy shared a bed with her parents, and Cavill would wake up in the middle of the night to shove a thermometer in her ear. "I probably bought about three or four different thermometers, because I needed to have the most accurate one so I could keep track of her temperature," she said.

Nervous to leave her alone, Cavill began avoiding social situations. 

"On the night that the first one happened, we had been out socialising. So, in my head, I thought, 'If I don't do that again, then it won't happen again.' It's not logical, but that is how debilitating my anxiety was getting. I wasn't making sense.

"I struggled so much. Some of the anxiety was justified, but the feeling of helplessness was what I needed to overcome."

A pivotal moment came for Cavill when she and Adam were looking at expanding their family.

"I wanted to have another baby, but I knew that I couldn't with how bad my anxiety was," she said. "I didn't want to leave the house. I didn't want to be away from her. I was just so anxious."

Something had to change.

"I started worrying about her choking, I started worrying about her drowning," Cavill said. Image: Supplied.

That's when a family friend suggested a first aid course.

"It was such a turning point for me," Cavill told Mamamia, adding that she has also spoken to a therapist and been on anxiety medication.

"There was a whole section [in the first aid course] on febrile seizures. Having more of an understanding of it, as well as learning CPR and what to do if she were to choke, what to look out for with rashes, and all of the things that I had let my mind run rampant with, was so helpful."

As far as Emmy's seizures, Cavill sought out a paediatrician who discovered that the toddler had chronically inflamed tonsils and adenoids.

"It's common in kids, but hers was making her so horrendously sick that any bug or virus would cause her to go downhill so quickly," Cavill explained. "So when she was three-and-a-half, we had her tonsils and adenoids removed. And ever since then, she has not had another seizure."

It was a surprising discovery for the parents, who had tested Emmy for epilepsy and other disorders. 

"If you had said to me, your daughter is having seizures because her tonsils are inflamed, I would have not believed you."

Cavill has since teamed up with Australia Wide First Aid to encourage parents to take a first aid course.

"One of the things that broke my heart is that only one in 10 Aussies have ever administered CPR on a child or baby," Cavill said.

"Obviously you'd never, ever want to — it is one of the scariest things in the whole world. But I think the scariest thing is not knowing how to do it."

Feature Image: Supplied.