HMM: What is SADS? Healthy young people dying from Sudden Adult Death Syndrome. “Sudden Adult Death Syndrome, or Sudden Arrhythmic Death Syndrome (SADS), is an ‘umbrella term to describe unexpected deaths in young people,’ usually under 40, when a post-mortem can find no obvious cause of death. . . . In the US, approximately 210,000 people die suddenly and unexpectedly each year due to sudden cardiac arrest, according to the American Heart Association.”