A fit 37-year-old got out of breath on a hiking trail at a national park. He had a rare and deadly form of altitude sickness.

• NBC journalist Morgan Chesky developed a fever, fatigue, and difficulty breathing on a hiking trip.
• After taking an ambulance to a hospital, he was diagnosed with high altitude pulmonary edema.

When Morgan Chesky, an NBC broadcaster based in Dallas, developed a fever after hiking Bryce Canyon in Utah, he figured a good night's sleep would cure it.

The 37-year-old journalist had "painstakingly planned" his multi-day trip with a "legendary crew," he wrote on Instagram, and had hiked more difficult, higher-elevation trails before.

But the next day while hiking at Zion National Park, Chesky said he became frustrated that he couldn't catch his breath. Even "a slow pace caused my pulse to spike. I got angry," he wrote. "When my uncle grabbed my pack, I let him take it and finished the trail, too weak to even celebrate."

Still, Chesky hoped it would pass with Tylenol and some sleep.

"But when I woke up worse, I caved. After hearing my symptoms at Urgent Care, they tested my pulse ox (blood oxygen saturation). Normal is 95-100 percent. Mine read 58," he said. "That's when they called the ambulance."

Chesky had a dangerous form of altitude sickness

At Cedar City Hospital in Utah, Chesky learned he had a condition called high altitude pulmonary edema, or HAPE, a severe form of altitude sickness. According to the National Library of Medicine (NLM), the condition tends to occur when people living in low elevations ascend rapidly to altitudes above 2,500 meters, or about 8,200 feet.

Doing so can put pressure on the blood vessels in the lungs, forcing fluid into lung tissue and the small air sacs of the lungs called the alveoli, the Mayo Clinic says. Symptoms typically begin two to five days after arriving at altitude and can first include a cough, fatigue, and difficulty breathing during physical activity, and progress to bluish skin and trouble breathing even at rest.

Left untreated, it can kill 50% of those affected, another NLM report says.

Bryce and Zion aren't quite 9,000 feet, and Chesky said he'd hiked at higher elevations of 14,000 feet before with no problem. But doctors at the hospital told him that didn't matter — even a cold that he didn't realize he had may have put him at risk. Men also seem more prone to the condition, which doesn't seem to spare people who are physically fit, the NLM says.

It's a good thing that Chesky went to the hospital when he did."When my lungs started to fill with fluid, it forced my heart to work harder, causing my pulse to skyrocket," Chesky said.

Hospital staffers told Chesky he could have passed out or suffered a cardiac arrest had he waited longer for treatment.
"Hard pass," wrote Chesky, who said he was treated with oxygen, blood thinners, and "stellar care" over 24 hours. "I'm not home yet, but hope to see y'all at a lower elevation soon," he added.

Prevent HAPE while hiking this summer

Research suggests that HAPE is rare in tourists, and most often affects mountaineers and climbers who are pursuing high-altitude climbs. But it's good for all hikers to be prepared.

According to the NLM, adventurers can lower their risk by giving themselves time to acclimate to higher altitudes, sleeping at lower altitudes, and avoiding alcohol, salt, and sleeping pills at higher elevations.

If you do experience symptoms, getting oxygen — be it by descending quickly, receiving supplemental oxygen, or both — is key.