Hey Recluse, hope you're doing okay - I had heart pains like that a while back, due to a bunch of stress and depression.
My heart eventually started doing weird things, skipping beats, and then when I tried to sleep it was like my brain wasn't getting enough oxygen, I'd get jerked awake as soon as I started drifting off. I thought my heart wasn't working right, so went to the ER, but everything turned out normal.
The body can do weird things under stress, like your muscles can get really tense in your chest and neck, even though you're not aware of it, and interfere with your heart working right and blood flow, etc. I remember even trying to meditate and relax, but it was still happening, so I thought for sure it wasn't just muscle tension, but it was. I wound up going on paxil, which helped a lot after a day or two.
In the meantime, see if you can relax the muscles of your chest. Like try taking some deep breaths and holding them, it might help make you more aware of the muscle tension, if that's what is causing it.