KATHMANDU, Nepal — When Geoffrey Chang, an Australian trekker heading to Mount Everest Base Camp, woke up with chest pain, his Nepali guide pushed immediately for a medical evacuation, saying he had a serious case of acute mountain sickness.

But the next morning, Mr. Chang was feeling better, and his oxygen levels had come back to acceptable levels, he said. His travel companion, Michelle Tjondro, asked the guide if they could simply rest that day or walk down like others with similar symptoms.

That’s when the red flags started to pile up.

The guide pushed aside those suggestions, continuing to press for a costly helicopter evacuation. Afterward, at a hospital marketed to foreigners in Kathmandu, Nepal’s capital, Mr. Chang’s passport was confiscated for several days, he said, and as the bill rose, a doctor told him his symptoms would need to be exaggerated in order to have insurance pay for his stay.