On October 19, Chelsea Ake-Salvacion was busy closing up shop at the cryotherapy spa in Nevada she helped manage. Alone and worn out from a long day, she decided to enter a cryochamber and soothe her sore muscles before heading home.

Cryotherapy—a relatively exclusive experience most used by athletes and celebrities—involves exposing your body to extremely low temperatures for a short amount of time. The benefits, though unverified by any one medical body, range from increased energy and libido to faster metabolism.

“The skin reacts to the cold and sends messages to the brain that acts as a stimulant to the regulatory functions of the body,” according to Cryohealthcare.com. “The skin exposure to the extreme temperatures also triggers the release of anti-inflammatory molecules and endorphins.”

Ake-Salvacion, 24, never exited the cryochamber. She was discovered dead the following morning.

“When they found her,” her uncle said in an interview, “she was rock solid frozen.”

Since there were no security cameras in the cryochamber room, nobody knows what happened to Ake-Salvacion—only exacerbating the mystery around an already-unclear procedure. However, coroners confirmed last week that Ake-Salvacion died by “asphyxia in an oxygen-poor environment.”

“Investigators initially ruled her death as a result of ‘operator error,’ but this assertion is emphatically rejected by her relatives,” NYMag reported. According to Cryohealthcare.com, the doors of a walk-in cryochamber are never locked and clients are free to enter and exit as they wish.

Family members say Ake-Salvacion was highly skilled in her profession and even working toward opening a cryotherapy spa in her native Hawaii.

While the merits of cryotherapy for human health have yet to be proven, there are practical uses for liquid nitrogen in analytical science: namely, as a cooling agent for gas chromatography ovens to attain sub-ambient temperatures in the analysis of refrigerant gases.