Arizona heat almost killed Lois Nigrin. Her coma, burns, and medical bills show the dangers of heat that many Americans face today.

This article is part of Insider's "The True Cost of Extreme Weather" project. Read more here.

When Lois Nigrin flew to Arizona with her husband, Joe, to celebrate the 30th anniversary of their first date, she never imagined she might not make it home.

But one miscalculation on a hot day would soon leave her in a coma. Her legs, buttocks, back, and head would have third-degree burns. Her organs would start to fail. Her kids would fly in to say their goodbyes.

"I don't think I had a true understanding of what heatstroke was," Lois Nigrin told Insider. "I had no idea that it could kill you."

Lois Nigrin is a teacher in Nebraska. She was 54 and healthy in June 2019 when, about 9 a.m., she and her husband started to hike up Camelback Mountain, a brown outcropping that rises 1,400 feet above Phoenix.

She grew up on a farm, working in the fields with her dad. She's no stranger to heat. What's more, she and her husband had been training for this hike, knowing it would be hot.

They brought plenty of water with them, though they didn't bring electrolytes. They had hiked Camelback before, several years prior, but that was in October.

Phoenix was 107 degrees Fahrenheit that day. That was also Lois Nigrin's internal temperature a few hours later when a helicopter lifted her off the mountain.

The hike went wrong quickly

As Lois and Joe Nigrin neared the top of the mountain, under the glaring sun, they saw people scrambling up rocky cliffs to the peak ahead of them. Lois Nigrin was feeling tired and didn't want to climb the rocks, so they turned around.

On their descent, two other hikers asked the couple to take their picture, then returned the favor. Lois Nigrin has no memory of that interaction, even when she looks at the photo.

The last thing she remembers is spotting a small tree, telling her husband she was "just so hot," and asking to pause in its shade.

According to Joe Nigrin, they took a break there and then kept walking down. He was getting worried. She was talking about her legs feeling like rubber. He started to pour water over her head and back. She insisted she was fine, but then she was leaning on him until he was basically carrying her.

She didn't realize it at the time, but her body could no longer regulate its temperature. She was succumbing to heatstroke, the most serious heat-related illness.

Finally, she told him to go get help.

"I didn't want to leave her there to die, but she was insistent that she couldn't get down the mountain," Joe Nigrin said.

From helicopter to ambulance, to another ambulance

At the bottom of the mountain, Joe Nigrin found a ranger, who took off up the mountain toward Lois. An ambulance arrived, and the EMTs followed where the ranger had gone.

They found her unconscious lying on a large boulder that was so hot it was burning her skin. First responders lifted her into a helicopter, which carried her to a parking lot at the base of the mountain, where an ambulance took her to the nearest hospital. Joe Nigrin followed in the couple's rental car.

According to Lois Nigrin, when she arrived at the emergency department, the doctors quickly determined she couldn't stay there. She had to go to a burn center.

So another ambulance took her to the Arizona Burn Center. In the heat waves of the past two summers, the institution has been overwhelmed with patients who get heatstroke in record temperatures or sustain burns from touching pavement.

In June, July, and August last year, 85 people were admitted to the Arizona Burn Center with heat-related burns, and seven of them died from their injuries. Dr. Kevin Foster, the center's director, told Insider that he expected this summer's toll to end up even higher. Though June was relatively cool, "July was absolutely hellish," he said, adding that the center admitted about 50 patients that month.

Overall, across the planet, average temperatures are rising due to humans' emissions of heat-trapping gases like carbon dioxide, which mostly comes from burning fossil fuels for energy. Hotspots like Phoenix are suffering increasingly brutal summer heat as a result, putting more people at risk for health emergencies like heatstroke. Last week, NASA announced that this summer was the hottest since global record keeping began in 1880.

The type of heat that nearly killed Lois Nigrin could add $1 billion every summer to US health care costs for things like emergency-department visits, according to an estimate from the Center for American Progress.

The Nigrins know the ordeal that could lie ahead for the victims of heat. Getting to the hospital is just the beginning. For Lois Nigrin, that began weeks of struggling to survive, months of therapy and skin grafts, and a mountain of bills to pay.

As Lois' organs began to shut down, doctors said she likely wouldn't survive

The morning after the disastrous hike, at the burn center, Joe Nigrin said a doctor told him to call any family who would want to see his wife and get them there as quickly as possible.

"I told him that, 'Well, our whole family is 1,500 miles away in the Midwest,' and he said, 'I would strongly suggest they get out here,'" Joe Nigrin said.

Lois Nigrin was poised to die that night.

Friends helped their four children arrange flights from Nebraska and places to stay in Phoenix. Lois Nigrin's sister flew in from New Mexico. Everyone was there by the evening.

She survived the night. But as her organs threatened to fail, she was transferred to the intensive-care unit at a local hospital. Healthcare workers employed more machines and tubes to keep her alive. A ventilator breathed for her. A dialysis machine took over for her kidneys.

In the ICU, confusion and hallucinations tormented Lois

Lois Nigrin didn't die. Instead, she slowly emerged from her medically induced coma.

She said she remembered little snippets from this time: her husband sitting next to her, her kids telling her to breathe in through her nose and out through her mouth. They later told her she was gasping for air after the ICU workers removed the ventilator tube from her airway.

She was hallucinating: children in the hallway, stuffed animals in her bed. At one point, she noticed that her hand was glowing red. That scared her.

"What's wrong with my hand?" she wondered.

"I remember thinking I would move my hand and try to see what it was, and I literally just could not even move my hand," she said. "Then I started thinking, 'Oh, my gosh, if it stops glowing, does that mean I've died?'"

Her husband later explained that she was seeing the red light of the blood-oxygen monitor clipped to her finger.

One day, she asked him when they were going home.

"I remember him just looking at me with tears in his eyes, going, 'Honey, you almost died. You can't go home,'" she said. "I was just like, 'I have no idea what you're talking about.'"

Her sense of time was wonky, too. One day, the nurses had her sit up for the first time. The next day, she thought, they tried to feed her applesauce, but she couldn't stomach it. Her daughter later told her she'd sat up and tried applesauce on the same day, at the same time.

"That's very hard as a person, to know that you went through stuff like that, and you can't make any sense of any of it," she said four years later, sitting in her classroom the day before her students arrived for the new school year. "And you can't understand why it happened. And you don't understand everything that was happening."

She added: "I just have had to let that all go. It's never going to be my job to understand this, because I can't."

All in all, she was in the ICU for 10 days.

Learning how to swallow, walk, and draw circles

Still, she couldn't go home yet. She couldn't swallow. She couldn't lift her arms. She had to relearn all that in another unit of the hospital, starting with eating applesauce as workers watched to make sure she didn't choke.

Her caregivers were helping revive her brain, too. They would tell her a simple story then ask her questions about it. They had her balance a checkbook, she said.

At one point, Lois Nigrin said, they asked her to draw a clock showing the time 3 o'clock. No problem, she thought. But she couldn't even draw a circle.

Sometimes she touched the back of her head and came away with clumps of hair. She was burned there, too.

Over a week, she worked her way up to eating crackers. She regained her sense of time, lost the hallucinations, and came to understand what had happened to her.

When she could walk to the nurse's station and back by herself, they sent her to a rehabilitation center. For another week, she worked on climbing the stairs, getting in and out of a car, and her hand-eye coordination.

Finally, she returned to Nebraska.

"Probably the best thing that I ever felt was that airplane landing and being back home," Joe Nigrin said. "Knowing my best friend was back home was probably the best thing."

Rehab continued there, and Lois Nigrin went to a hospital to get skin grafted from her thighs onto the burns on her lower legs, buttocks, and back.

In mid-August, she returned to work for the beginning of the school year, cane in hand and legs wrapped in bandages. Her daughters set up her classroom for her, and she started out part time, easing her way back to full time.

The Nigrins lost time, wages, and birthdays, but they kept Lois

Lois Nigrin's legs are scarred from the burns and grafts, so she doesn't wear shorts anymore. She has some bald spots where her head was burned. She doesn't have as much energy as she used to. She walks more carefully. She has more trouble remembering names, though she's not sure whether that's from the heatstroke or because she's getting older.

The bills had started arriving in the mail while she was still in the hospital. Between the helicopter, ambulances, emergency care, the ICU, rehab, and skin grafts, the whole ordeal cost the Nigrins more than $4,000 in medical bills; the family spent about $2,000 more to bring everybody to Phoenix. The couple's health insurance covered more than $280,000 of expenses related to the heatstroke, according to documents reviewed by Insider.

The whole family lost wages while they were stuck in Arizona. Lois Nigrin missed two of her kids' birthdays, as well as her own. She had planned to help her son move into a new apartment, but that time came and went while she was sick.

Still, she said, "I look back on it now, and I think how lucky I am."

Her daughter just graduated from high school, and her son finished law school. Her other son got married this month — "all the great things that I would have missed out on if it hadn't been for wonderful doctors and so many people praying for me," Lois Nigrin said, adding: "So I'm a very, very lucky person."