It starts suddenly, without warning. Maybe a twinge, or a slow, steady pressure in your chest. At first, it's not quite painful, but the discomfort is there nonetheless. You break out in a cold sweat, as if someone has just walked over your grave.

You feel somewhat nervous now, trying to place the last time you felt like this. But you can't remember a time when you ever felt like this and why does your arm and neck hurt so much all of a sudden?

You have stopped whatever it is you're doing, because whatever this is that's happening to you has grabbed your full attention. The pressure in your chest is still building, and you're breathing like you've just run the marathon. Your brain is spinning, trying to make sense of the signals that are coming from your body. Then, with a wave of nausea, you realize that everything is spinning.

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