Question: Why should one be afraid of being reborn in a lower realm like hell if one does not remember anything from one’s past life?
Answer: If one knows one is going to hell later, one will be terrified now. If one is in hell now, one will be terrified now too. Therefore, the true terror is more in terms of now and the future; not the past. Healthy fear is good as it leads to moral shame from doing evil; without which there will be more evil done.