Yes, it can be dangerous and life threatening. It may cause heart attacks and sudden cardiac arrest. Pharmacological interventions can reduce these factors.

Not necessarily. Typical cardiac testing may show signs by showing some ischemia, but is often hard to diagnose with the usual cardiac testing.

This is possibly the hardest question of all. There is no simple answer unfortunately, and no rhyme or reason either. It may be hereditary or it may be completely random.

There are many factors to consider when answering this question. How do you define normal? The answer also depends on your lifestyle and your condition. You will have good days and bad days. You may have to make changes from day to day. You may have to change your current lifestyle. Listen to what your body tells you and rest when you need to. Know your limitations.