One idea for you. I read in a fitness book that some athletes like to maintain a diet where they cycle between high protein and high carbohydrates. If you do this, what tends to happen is that when you are on the high protein portion of the cycle you start feeling "spacey". The problem corrects itself when you return to the carbohydrate portion of the cycle.
Just a thought.
Should read as follows, auto correction changed it:
"not uncommonly as a crushing feeling in the chest, or pain radiating up the neck..."
I wrote a reply to your question last night, but using my tablet to do it, bumped the screen and shut the window before I had a chance to send. We have an Ailmentary Canal (and associated organs), essentially a tube starting at the mouth and going completely through to the other end. In a tubular organ, food is moved by a process known as Peristalsis, this is a process where a contraction of the muscles in the tube rhythmically move from a closer point to the mouth to a more distant point, and by doing such move the contents of that particular section further away from the mouth. It's fortunate that it works this way, everything still works regardless of the position we're in, and it works for astronauts too, so that we don't need gravity for digestion.
Those of us that are anxiety prone (and sometimes when we're getting sick with a stomach bug, or in reaction to something we ate that disagrees with us) can have particularly strong peristalsis, and we may be able to significantly feel it, and often others can hear it, even from across the room. This phenomenon is known as Borborygmus.
http://wordsmith.org/words/borborygmus.html
It may be the peristalsis/borborygmus that you feel in your chest.
As to the heart, if you're concerned, it never hurts to see a doctor. Heart issues can manifest as an arrhythmia (with or without underlying heart disease), or pain (usually, though not always, associated with Coronary Artery Disease or "CAD"), not uncommonly advanced crushing feeling in the chest, or pain radiating up the neck, or down the arms, and not uncommonly pain in the fingers, especially, if memory serves me correctly, the 2nd and the 3rd fingers.
Symptoms, even without pain, can include shortness of breath, and dizziness and lightheadedness, but anxiety can cause similar symptoms to these.
Some problems with the heart are due to rhythm issues, with or without heart disease, or can be from coronary heart disease, from structural issues, such as with the valves in the heart, or from congenital issues that may have gone undetected. What you described doesn't sound to me to be heart related, but no one, including doctors, can diagnose you over the internet.
Why don't you just make an appointment for a physical examination at your Family Doctor, tell him your concerns, and ask if it's OK to return to the gym?