Hello Jesse, welcome to the forum. I hope you will like it here
I am sorry to be the bearer of bad news but the only situations in which I have heard this happened was while people were having early signs of a heart disease. I would advise you to go back to your doctor and request a 'stress-test'. I am sure that if this will happen when performing this he will know which other tests you should be taking and what to check out.
Good luck, and don't panic, it is good to catch this when it has not yet developed in a full fletched heart disease