Sudden cardiac death can be hereditary. Usually they are due to abnormal rhythm of the heart - Arrhythmia. You need to undergo a Holter monitoring, a test wherein we tie a belt and record your ECG for 24 hours. The episode of fainting, dizziness and blackout could be due to an episode of arrhythmia. We also need to look for Cardiomyopathy, for which I believe an Echocardiography has already been done. If all these tests are normal, we need to rule out simple things like vasovagal syncope, for which we need to do a Tilt table test.