Quote Originally Posted by Supernova View Post
Here's my 2 cents:

As for the rapid/strong heartbeat, I've heard numerous people bring this up, and I've experienced it myself. It seems to happen when transitioning from waking to sleep when you're trying to enter sleep paralysis. I don't know of any physiological reason that might cause it, and I've heard some claim that the pounding heart is just a hallucination. I've not ever heard anything on it from a definitive source, but that's what I know.
Whenever I have experienced sleep paralysis the first feelings I get are hallucinations that I cannot breathe, and I find it very difficult not to end up hyperventilating. I'm not sure if the rapid heart beat I am feeling started off as a hallucination but by the time I break out of sleep paralysis I definitely have a rapid heart beat from the fear of suffocating.