Yes. Your tooth is part of your body. A hole signifies destruction. As in the phrase, it's just the tip of the iceberg, you have no way of knowing how deep the hole or how big the problem. Untreated cavities lead to loss of teeth and infections. Infections can kill you. I hope this answered your question.
Sure. People believe that if there is no pain there is no problem. High blood pressure, diabetes, and many cancers are painless until it is too late. Why are you waiting to make an appointment to evaluate what the tooth needs? It isn't going to fix itself, and the longer you wait, the better the chance of infection, which is detrimental to your health.