I work in a hospital on a cardiac unit. And this is an extremely important sentence to remember:
call the Paramedics if ANYTHING is unpleasantly happening that you've not felt before. It is better to have a 'false alarm' visitation than to risk your life guessing what it might be!
Luckily for a lot of our patients, it is a "false alarm visit". But that is what we are there for!!!! NEVER be embarrassed that it could be a false alarm. Be GRATEFUL!!! If is a heart attack, you just don't want to take a chance with your life.