Gosh, I don't know. Ironically, I'm having left hand problems right now too! Except I know why: it's self-inflicted (but not purposeful). I use the mouse with my left hand and I think I've developed a repetitive stress injury (I do hours of imaging via a specialised programme). Ouch.
Firstly when I read your post I thought the same. Then you wrote that you're experiencing symptoms even when you're not using your hand/arm, with indicates something else. If you are in otherwise good health, with no other symptoms, I really doubt you're prone to a heart attack but you should see your GP right away. Maybe you have a pinched nerve? Or an orthotic problem such that your bones aren't aligned properly. Anyhow, I hope your arm feels better soon and your doctor can sort out your mystery symptoms.
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The ones who say “You can’t” and “You won’t” are probably the ones scared that you will. - Unknown