[5] Medical examiners have taken into account various factors, such as nutrition, toxicology, heart disease, metabolism, and genetics.

[3] However, studies reveal that people were known to have had symptoms within the week before the terminal event such as chest pain at ~52% of patients, dyspnea at ~22%, and syncope at ~7%.

A 2011 autopsy-based study found that sudden death was attributed to a cardiac condition in 79.3% of cases, and was unexplained in 20.7%.

A 2011 retrospective cohort study using demographic and autopsy data for a 10-year period comprising 15.2 million person-years of active surveillance suggested that prevention of sudden death in young adults should focus on evaluation for causes known to be associated with SCD (e.g., primary arrhythmia) among those under 35 years old, and emphasise atherosclerotic coronary disease in those older.

[1] A national SADS study in England, funded by the British Heart Foundation, reported results in a 2007 journal article published in Health.

[17] The condition appears to primarily affect young Hmong men from Laos (median age 33)[2] and Northeastern Thailand (where the population is mainly of Laotian descent).

[18][19] Laotian Hmongs were chosen for the study because they had one of the highest sudden death rates in the United States while sleeping.

The location that was picked for this study was in Ban Vinai in the Loei Province, which is approximately 15 kilometers from the Lao border.

Ban Vinai was the location chosen because it had 33,000 refugees in 1982, and the largest number of recorded SADS deaths.

The interviews were open ended and allowed the person who was next of kin to describe what they witnessed and what preceding events they thought were relevant to the victim's death.

[2] During the 1970s and 1980s, when an outbreak of this syndrome began, many Southeast Asians were not able to worship properly due to the Laotian Civil War.

These attacks induce a nightmare that leads to sleep paralysis, in which the victim is conscious and experiencing pressure on the chest.

[clarification needed] The study author suggested that the Hmong who died were killed by their own beliefs in the spiritual world, otherwise known as nocturnal pressing spirit attacks.

This phenomenon is known among the Hmong people of Laos,[20] who ascribe these deaths to a malign spirit, dab tsuam (pronounced "dah chua"), said to take the form of a jealous woman.