Last year med student here, sudden cardiac arrest commonly occur in young people. Apart from infectious myocarditis which you might notice as fatigue and reduced performance after you’ve suffered a respiratory infection, hypertrophic myocardiopathy and especially hypertrophic obstructive cardiomyopathy is often hereditary and can be mortal without showing prior symptoms. That’s why after a patient’s death you usually examine their broader family if HOCM was the cause as it can be detected via ultrasound and treated pharmacologically or interventionally (injecting alcohol in the obstructive parts or implanting a defibrillator).