An adult version of sudden infant death could be responsible for a large number of fatalities each year, researchers say.
Undiagnosed cardiac problems can cause sudden death
Researchers from the British Heart Foundation (BHF) say if the condition was given an official label, such as sudden adult death syndrome, deaths could be officially certified and investigated.
After cot deaths were officially labelled as the sudden infant death syndrome, it was possible to collate information, identify possible causes and act to protect babies.
The move led to a 70% fall in the number of deaths over a 10 years.
The new study estimates that in England, 3,500 apparently healthy adults die suddenly each year.
In such cases it can be very difficult to identify a precise cause of death
In about 150 of these no cause can be identified. Some could be due to inherited electrical abnormalities in the heart, but these can only be detected when people are alive, and not after death.
The BHF researchers say the lack of a label means bereaved families have no reason for the loss of their loved one, and it is difficult to be sure how many people are really affected by the condition.
The BHF is now funding more research looking at potential causes of unexplained adult death.
Dr Tim Bowker, associate medical director at the BHF, who is leading the research, said: "It has long been recognised that there are occasions when an apparently previously healthy adult dies suddenly and unexpectedly and any abnormalities found at post-mortem are minimal or non-existent.
"In such cases it can be very difficult to identify a precise cause of death.
"This leads us to question whether these deaths are rare or represent the tip of a larger iceberg."
He added: "Our findings suggest to us that these deaths should be classed as the adult equivalent of the sudden infant death syndrome.
"If the condition is more frequent that we suspect - particularly if across the country pathologists and coroners are using different words to describe the cause of death - we need to give the condition a 'name' to help us gain a greater understanding of the scale of the problem."
Dr Bowker added; "Not until it is accepted practice to identify all these unexplained deaths and to label them as such, will it become possible to study them systematically, identify their causes and find ways of preventing them from occurring - and the name we propose is 'sudden adult death syndrome' or 'SADS'."
Professor Sir Charles George, medical director of the BHF, said: "This study takes us another step closer to unravelling the mystery that surrounds the tragedy of healthy adults dying prematurely from sudden adult death.
"Because the 'alarm bells' only start ringing after the death of a seemingly well adult, we hope our new findings will encourage people to look back into their family's medical history and to think about whether any close relatives may have died young from unexplained causes."
But he said: "At this stage, there is not sufficient evidence to back calls for population screening.
"What is needed is further research and accurate pathology to assess the scale of the problem and widespread support and follow up of surviving relatives."
The research is published in the Quarterly Journal of Medicine.