What else can cause very mild arm pain mild chest pain and nausea besides a heart attack? i've had discomfort all day but don't want to overreact...

Get checked out: The symptoms you describe could certainly be explained by a heart attack. Not everyone has the "classic" symptoms of crushing chest pain when they have a heart attack. There are certainly other possibilities, but since it is unclear the safest thing to do would be to get evaluated by a physician as soon as possible.

Don't contemplate: This can be potentially acute -- call 911 and go to the nearest er.