I have read this before, but unless you're being told this information from a medical professional or someone with verifiable authority in the field, it's probably best to ignore it, especially if it came from Facebook of all places. By any chance was your second statement about the parasympathetic nervous system from Yahoo! answers?
Besides that, the two statements you posted are somewhat contradictory. The first says the adrenaline release stuns the heart and the second says it's actually the parasympathetic nervous system rebounding to the spike in fear causing the heart rate and blood pressure to drop. I don't know enough to tell you otherwise, but adrenaline is there to protect you from danger, not kill you. In the past I've had severe panic attacks where my heart rate has been maintained at rates of 200+ for prolonged periods and nothing ever happened. It certainly didn't shock or stun my heart to the point of failure and no rebound calming effect took place in response to my extreme fear.
I know there are some animals that play dead, but actually I don't remember ever seeing a scared person do this. Do humans play dead to ward off predators? How does playing dead even work anyway, when a hungry lion is chasing you down on the planes? I'm off the impression that most of the predators (big cats/bears/wild dogs/etc.) humans are vulnerable to are going to eat you dead or alive, so what good is it for humans to have a "play dead" mechanism? I think that idea is wrong.
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