I am sure you would know the difference. With the ones the mind makes up they don't cause the real effects of a real illness. Take a person who always fears rabies. They might have the fear that they have rabies. But they won't have the actual real symptoms of a person who really does have rabies. With other illnesses there are symptoms which a mock illness can not bring about. You might have the fear but not the symptoms. If you had the symptoms I would suggest a doctor's visit.