There were pathologies that were not diagnosed during life due to the lack of manifestations of any complaints. For example, vascular abnormalities, cardiac irregularities, brain damage, latent infections and prolonged intoxication.
If a person is absolutely healthy, then by itself his heart cannot suddenly stop, because there is not the slightest reason for this. Another thing is that a huge number of factors can lead to its stopping, which I cannot list (I am too incompetent in this matter). In short, succumbing to logic, a healthy person will die only if someone or something kills him)
I must note that such people are probably healthy only at first glance. Some of them manage to make a diagnosis during their lifetime, the relatives of the deceased learn about the problems of others from the pathologist. As a rule, such death occurs in connection with the further inability of the heart muscle to function normally. It can be caused by a number of various factors from long-term alcohol dependence to genetically determined syndromes. A detailed description of the most common causes of sudden death is given here.
In recent years, statistics on sudden death syndrome (and this is the name given to this phenomenon) has sharply deteriorated. It reflects the lack of attention of the younger generation to their own health, because such simple things as a correct daily routine, limiting alcoholic beverages and controlling their own mental state to avoid stress could significantly prolong life.