The LA Times carried a story about an attorney who arrested and was saved by his staff members. See
Each of us as more than a ten percent chance of seeing - at least once in our lifetime - a family member, a friend, or an associate die of a cardiac arrest. When that happens, the victim is clinically dead, and will almost certainly stay dead unless someone sees that person die, calls 911, begins CPR, and - if one is available - promptly defibrillates the victim's heart with an AED.
When one of the possible outcomes of an event (for example, a cardiac arrest) is, in your mind, truly unacceptable, you need to view the odds of that happening as being 100% and prepare to deal with it when the arrest happens.