http://www.webmd.com/sleep-disorders/guide/sleep-paralysis
I get this, specifically the hypnopompic kind (that's when it happens upon waking, as opposed to when you're drifting off).
@Anarchy, you're referring to the hypnic jerk (
http://en.wikipedia.org/wiki/Hypnic_jerk), when you refer to the possibly vestigial remainder of a "don't fall out of the tree" impulse. Just for fun, here's an article about what you're talking about, re REM sleep (if anyone else wants to read it)
Dead Link Removed
Anyway,
@Go Hungry, it really is common to have a hallucination when in sleep paralysis - sometimes it's visual, sometimes it's only sensory. When this happens to me, I either see someone in the corner of the room, or I have someone sitting on my chest. It's really hard to breathe when you're in sleep paralysis, because you aren't in control of what your body is doing, basically - I'm curious what you experienced in this regard since you were using a CPAP.
Mine tend to last a few minutes at the most. Stress is supposed to be a huge factor in developing sleep paralysis. But, if you didn't feel a pretty big surge of panic, it might not have been a full on sleep-paralysis, it could have just been a rough transition out of REM coupled with some dream/reality crossover, especially if you were in a dark room.