Ms Tippi Clark, 24, a nutritionist in Manhattan, was describing a mission that tested her endurance.
"You reach the peak and it's like, 'oh, my gosh, can I make it through the last 20 minutes?'," she said.
She was not talking about scaling a mountain but withstanding a 60-minute session of heat hovering around 69 deg C at HigherDOSE, an infrared sauna centre.
It uses heaters that emit infrared light waves that create heat in the body rather than heating the air. The idea is that one can stay in them much longer and sweat more.
Thanks to spa-like locations where one can perspire in private, and celebrity endorsements, the infrared sauna is looking like the latest wellness fad.
Infrared heating was pioneered in the mid-20th century for use in hos- pitals, mostly in Europe and Japan, to speed up the healing of wounds and to warm premature babies.
Units for personal use gradually gained a following, with adherents crediting time spent sweating with everything from weight loss and glowing skin to better sleep and detoxification. Paris-born Sophie Chiche, 49, who now lives in Los Angeles, could find an infrared sauna only in "a suntan salon-type with no bathroom, where I thought, 'I'm going to catch death every time I come here'."
Her solution was to open Shape House in 2012, which bills itself as an "urban sweat lodge". It uses an infrared heated sleeping bag.
Clients are encouraged to watch television instead of meditating.
They get lavender-scented towels during sweat sessions; oranges and tea are provided afterwards.
HigherDOSE (the caps stand for Dopamine, Oxytocin, Serotonin and Endorphins) is the creation of Ms Lauren Berlingeri, 30, a health coach, and Ms Katie Kaps, 31, a former investment banker.
Ms Berlingeri introduced Ms Kaps to infrared saunas, which she was sure would be the next big thing.
"I was a crazy workout freak and had issues with my nervous system, my skin and sleeping at night. Someone suggested I try an infrared sauna," said Ms Kaps. "It was the best sweat I've ever had. I felt like I had just run 10km."
The duo teamed up to install infrared systems at yoga studios.
At HigherDOSE, where rates start at US$45 (S$61) for 30 minutes, there are three rooms. Each has a wooden sauna, a sink and a large glass bottle of filtered water.
Ms Clark listens to guided meditations or tango music while she sits in a sauna. "I feel safe and alone in a cocoon of warmth," she said.
Do the saunas have health benefits?
"We do not have data that shows one can sweat out toxins in any meaningful way," said Dr Catherine Forest, a clinical assistant professor at the Stanford University School of Medicine. "But people feel better after they sweat and think they look better, and that's worth a lot."
There may well be some medical benefits. "It may improve pulmonary function for people with asthma. Heat improves joint pain for people with arthritis," she said.
Regardless, the lithe women who populate the HigherDOSE Instagram account seem satisfied.
The comedian Chelsea Handler had an infrared sauna built in her bathroom. "I use it on average three times a week," she wrote in an e-mail. "It is more rejuvenating than anything else I've tried."
NEW YORK TIMES