A Quebec woman who died last summer after a reported spa detox treatment was actually a member of a self-improvement group practising risky therapy involving sweating and hyperventilation.

Radio-Canada's Enquête program has learned that Chantal Lavigne, 35, died from hyperthermia, after undergoing a nine-hour session of intense sweating at a home in rural Quebec in July 2011.

The session was part of a seminar called "Dying in Consciousness" led by a self-styled Quebec therapist.

Lavigne and eight other participants were covered in mud, wrapped in plastic and blankets and spent nine hours lying with their heads in boxes while being encouraged to hyperventilate.

Lavigne, 35, was eventually taken to hospital unconscious by ambulance, with a body temperature of 40.5 degrees. She died hours later. (Radio-Canada)

Lavigne was eventually taken to hospital unconscious by ambulance, with a body temperature of 40.5 degrees. She died hours later.

Normal human body temperature is 37.0 degrees.

The Quebec coroner in charge of the case said she died of hyperthermia — a medical emergency caused by failed thermoregulation, when the body produces or absorbs more heat than it can dissipate.

Given the conditions, more people could have died "in cooking them like that" said Dr. Gilles Sainton. "It could have been much worse."

The session was led by Gabrielle Fréchette, who has been offering self-improvement courses for 20 years, most recently at the Ferme Reine de la Paix, a country house near Drummondville.

She claims to be channelling Melchisedech, a figure mentioned in the Bible.

According to Fréchette, about 2,000 people have taken her courses, including Lavigne, who completed 85 different sessions at the cost of more than $18,900.

The group's practices raise troubling questions, according to Dianne Casoni, a criminologist at the University of Montreal.

"How is it possible that groups that have so much influence over people and sometimes put them at risk are not more closely watched?" asked Casoni, who studies self-help groups.

"The problem with these groups is they're not overseen by any institution or government department."

Fréchette and her group continued to offer sessions after Lavigne's death, and told Radio-Canada's Enquête program that she is completely booked until the end of February.

She also said she isn't responsible for Lavigne's death, and did her duty by calling 911.

Quebec provincial police, the Sûreté du Québec, said they expect to submit the results of their investigation into Lavigne's death to prosecutors in coming days.

After that, prosecutors will decide whether or not charges will be laid.

The room where the sweating session took place, seen here in a dramatic recreation. (Radio-Canada)