I used to have these episodes rather frequently. On several occasions in my thirties, I went to the hospital and got EKGs. Nothing ever showed up on them. Finally, a doctor told me they were esophageal spasms -- sort of like IBS, but in this case, my esophagus was cramping rather than my colon. When one of these things comes on, you'd swear you were showing multiple symptoms of a heart attack: pressure in the chest or arm, sometimes stabbing pain right through the chest or back on the left side, yada yada. Relaxing and deep breathing eventually brings a release, and the pain and pressure go away as if they had never been.
I haven't had one of these in a long time. I'm guessing that dealing with my recovery from surgery and the general stress of the holidays plus figuring out retirement all come into play. It's important to listen to your body. But it's also important to not take everything your body is telling you at face value.
I got out just for a bit yesterday evening and walked around the corner and back. It wore me out, but it felt good. I need to get outside and start building up my strength. Lazing around in the recliner isn't doing me any more good.