Dan, I can sense your frustration. Ignore the ■■■■■■■■ written above. In the first instance, I would purchase a blood pressure monitor (assuming you don’t already have one), and take a reading at various times through the day, and try and ascertain when it reaches its lowest point. If there is no dangerous low point and this was a truly one off event, could the thoughts of cancer in the family be so traumatic that the emotional stress altered the vagal tone? Only you could know that. Do you hold your breath in stressful situations? Consider that too. Good luck in getting through this.