On the morning of December 16, in Kampot province, a slight 17-year-old student named Pen Kunsotheara began to feel faint.

The ninth grader at Hun Sen Ang Sdok High School felt her fingers become numb. Soon she couldn’t feel her hands. As she struggled to breathe, Kunsotheara collapsed and blacked out.

Fourteen other students in the classroom – all girls – fell unconscious in quick succession.

The faintings didn’t stop.

Seven students collapsed the next day, then nine more the next week. On a single day in early January, 31 students passed out.

The mass incidents, which have affected only female students, have now been taking place for a month. And it has gotten worse, school officials say, with more and more girls not only fainting but – in a phenomenon not uncommon in a superstitious country like Cambodia – convulsing violently and issuing proclamations purported to come from the spirit world.

Kunsotheara, who has fainted four or five times more since the initial incident, said she was told by classmates that she appeared to have been possessed the last time she passed out.

“I could hear my mum calling me,” said Kunsotheara, speaking yesterday from her family’s small coffee shop. “But I could not speak.”

Garment workers fainting en masse in countries like Cambodia, Bangladesh and Malaysia have made headlines around the world, with labour advocates linking the phenomenon to poor working conditions.

But such explanations have been unable to explain mass faintings among schoolchildren, which have also been reported regularly in Asia, Africa and the UK and US.

Psychologists say the cases fit the description of “mass psychogenic illness”, which usually presents as dizziness or stomach-aches that spread from one person – almost always female – to others in her community without explanation.

At Kunsotheara’s school, in Angkor Chey district’s Samlanh commune, provincial medical experts were unable detect any health problems among the students.

Instead, villagers pointed to an evil spirit linked to the Khmer Rouge-era burial site next door, where thousands of bodies are said to have been buried without coffins or proper ceremonies. Later, a primary school was built on the land.

“The doctors said that they had low blood sugar, but we questioned why it happened to so many people, and only for girls,” said school headmaster Sao Narith. “At that time, I thought, ‘This is not related to spirits’. But now I’m starting to believe.”

All the students who fainted at Hun Sen Ang Sdok High School described experiencing similar symptoms – numbness, dizziness and difficulty breathing, sometimes with the feeling of their throat being clenched – before fading out of consciousness. Over the last week, more and more described going into an altered state, as if being possessed by a spirit.

And the spirit, as they tell it, appears angry.

One supposedly possessed female student, speaking in an unusually deep voice, demanded that the upper floor of the new building be cleaned – not just swept, as it usually was, but washed down. The school did as it was told.

Another was filmed at the commune health centre, writhing on a bed and screaming “Why do you keep mocking?” – apparently referring to a teacher in the school who had made fun of students who believe in ghosts.

School officials scheduled an elaborate prayer ceremony for Wednesday involving seven monks from seven different pagodas blessing every room of the school. But three days beforehand, a female student collapsed and began shaking, according to Narith. In a booming voice, the student demanded the ceremony be held a day earlier. They moved it up.

Then, during the ceremony, one of the student dancers fainted. Footage shows the girl falling to her knees as she is supported by classmates, head rolling back and chest heaving violently. Witnesses later said a spirit appeared to speak through her body and demanded traditional dancing take place at the school at 7am on every holy day – four days a month.

Narith argued with the spirit, pointing out that school starts at 7am.

“Now we are thinking about it,” he said in an interview yesterday. “It is not really easy to do. We have to prepare the clothes and music and money, too.”

What could explain these mysteries, if not evil spirits, is difficult to say. An increasing number of researchers who study mass psychogenic illness say the fainting spells may have less to do with ghosts and more to do with psychological stress from oppressive living or working environments, especially in communities with histories of trauma.

Robert Bartholomew, an Australian sociologist who documented more than 3,500 incidences of mass psychogenic illness around the world, said his research points to these fainting spells as a subconscious form “of ritualised rebellion” – a kind of collective protest that allows young women to bargain with authority figures without facing the consequences.

In a society where young women are often taught not to speak out, the spirit “deflects the blame”, Bartholomew said. “It’s not the student that’s complaining, it’s the spirit speaking through the student.”

In most schools, typical stressors are strict new rules imposed by school administrators or tension in the community.

“The mind speaks where the body can’t,” Bartholomew said.

He is backed up by another Australian researcher named Maurice Eisenbruch, a Khmer-speaking psychologist who visited dozens of Cambodia garment factories that were the sites of mass faintings between 2009 and 2016.

In a roundabout way, Eisenbruch said, fainting garment workers have been able to temporarily shut down factories or force directors to improve conditions.

“Mass fainting seems to be an outcry of protest by disempowered workers whose misery is made more acute by their factory work,” Eisenbruch wrote.

And in the same way that faintings have sometimes led to better working conditions or higher wages, mass faintings in schools have also resulted in cancelled classes or relaxed student rules.

However, none of the girls yesterday described any tensions or anxieties at the school, which is located in a wealthy part of town where many teenagers own smartphones and motorbikes.

But Bartholomew said research suggests something is probably causing anxiety for the students. If one were to spend more time with them, cracks might start to appear, he said.

“It sounds to me like they need to just relax,” Bartholomew said, noting that most of the “spirit’s” demands seemed to be related to breaking up the monotony of the school day. “If [the school officials] want these outbreaks to go away, they need to compromise and they need to have a little more fun in their lives. I think if they do that, this will go away.”

Time will tell, but Narith is hopeful that the ceremony has done the job. Just two more girls have fainted since, and none did yesterday.

One of those two girls fainted at home. Her father came to the school that evening with an offering of bananas, Narith said. He also came with some news.

“I won’t come back again,” the spirit had shouted in a booming voice. “They have already given me everything I want.”