Hi,
This can happen with Autonomic neuropathy. The Autonomic nerve system can play havoc with all the automatic features of the body we don't need to think about to have happen, like heart, lungs, throat, digestive system and more. The interferance can be random and or permanent. I have some that have become permanent while more that are randomly occuring. My BP drops with excessive physical activity and has done for the last 2 years. The interferance from ANS is increasing with some features now permanent while yet others are still random and varied from day to day. Only once did it affect the heart, fortunately it is one of the organs that is least affected by ANS for me. I'm well aware that could change at any moment so I try to not overdo anything, everything in moderation suits me best now.
Cheers