If you don't know what it is, you've probably never experienced it. Or maybe you just didn't know that's what it's called.
Physiologically, sleep paralysis is closely related to the paralysis that occurs as a natural part of REM (rapid eye movement) sleep, which is known as REM atonia. Sleep paralysis occurs when the brain awakes from a REM state, but the body paralysis persists. This leaves the person fully conscious, but unable to move. The paralysis can last from several seconds to several minutes "after which the individual may experience panic symptoms and the realization that the distorted perceptions were false".In layman's terms, your conscience wakes up, but the rest of you doesn't. The result is basically dreaming awake.
This probably sounds fun, but it's often quite strange and usually frightening thanks to a mental conflict of knowing that you're not dreaming, but are experiencing dreamlike imagery, sounds, and feelings (which are often not pleasant to say the least).
Pressure on the chest is a common feeling, but I've never felt it.
What I do feel as a predecessor to the hallucinations every time, however, is an intense pulsing sensation in my head accompanied by ringing sounds. At this point, I make a choice to either go with it or try to break out by forcing a body part to move (which can be very difficult).
The pulsing can be best akinned to saying "ooooooo" and quickly but loudly saying "WA", where the oooo represents the ringing. It's also unpredictable.
Ultimately, though, it's harmless and far too interesting (albeit scary) to pass up every now and then.
UHHHHHHHHHHHHHHHHH long post is long.
Go ahead and share your sleep paralysis experiences.