So I think everyone who has made it into sleep paralysis has experienced the sensation that their heart is just pounding like crazy. Well I am here to tell you that it is purely a halucination. Your heart rate does not increase. How do I know? I got my wisdom teeth out today. I was hooked up to a heart monitor as per procedure, and they started me breathing nitrous oxide to calm me down. Guess what, as the nitrous took hold, it felt exactly like I was going into sleep paralysis, that kind of ballooning numbness that completely fills you up. I even got that insane heart-pounding sensation and I thought "the gas isn't helping..." But I noticed I could still faintly hear the heart monitor, and it was beeping very slow and normally. Far slower than the pounding sensation.

So. Proof that your heart rate does not increase like that during sleep paralysis.