MANILA: The death of a young actor in the Philippines last week has put the spotlight on a mystery ailment which kills healthy Asian men in their sleep.

Filipinos call it "bangungot" or the nightmare syndrome. Victims are heard moaning just before they die, which is usually in the middle of the night, doctors say.  Romantic hero Ricardo Yan died in his sleep last Friday at just 27 years of age.

Doctors said on Tuesday he died of haemorrhagic pancreatitis leading to cardiac arrest. But there was no word on why the ailment should strike an apparently healthy young man.

Yan was on holiday at a beach resort with a group of friends. Autopsy results showed he had drunk only a moderate amount of alcohol, equivalent to about two bottles of beer, prior to his death. There was no evidence he had taken any drugs.

Filipino doctors - who call bangungot the Sudden Unexplained Nocturnal Death syndrome - said it generally strikes men between 30 to 40 years of age, although the

youngest known victim was only 17. Women are usually not affected. "We have not autopsied any woman who died of bangungot," said Dr Edgardo Gueco, chief of the national police medico-legal division.

"Based on our observations, the victims had eaten heavily or drunk heavily before going to sleep," he said in a television interview.

What happened during sleep was a mystery because the bangungot victims never woke up, cardiologist Erdie Fadreguilan of the state-run Philippine General Hospital told Reuters.

"The findings were that something went wrong with the rhythm of the heart while they were sleeping," Fadreguilan said, citing results of autopsies of 328 bangungot cases in the Philippines from 1957 to 1987.

In their last moments, the victims were usually heard moaning or groaning in their sleep, as if suffering from "some form of agony", he said.

"We had no way of knowing what happened because they did not survive."

Stranger still, bangungot usually claims its victims at about 3 o'clock in the morning, doctors said.

Fadreguilan said studies show bangungot cases occurred mainly in Southeast Asian countries like the Philippines, Vietnam and Laos, but a similar illness had been reported among Japanese men.

In the United States, only Vietnamese refugees have suffered from the condition, he said, but spurned a theory it could have a cultural or hereditary explanation.

"Even if you move to different places, like the refugees going to the United States, the men can still suffer from it," Fadreguilan said.

"Whether they move outside of their home country does not decrease the risk of them suffering from it."

Local doctors believe a possible cause of the condition could be the high carbohydrate diet of Asians, who eat rice as their staple.

But no one has been able to pinpoint why rice should have any such effect on a select few or why millions are unaffected.

In Manila, thousands of unbelieving fans flocked to Yan's wake.

"This can't happen to him, this can't happen to me, this can't happen especially to him," Yan's long-time girlfriend actress Claudine Barretto told a television station. "I couldn't believe it." Reuters