Sleep Paralysis does occur in everyone during REM sleep. The Sleep Paralysis we're after is called Waking Sleep Paralysis. This is basically a state where your mind turns off specific neurons at the base of the spine, which in effect, numbs the body. Your brain shuts down many other neurons during sleep. By doing this it enables the neurons to eliminate natural neurotoxic build up through out the day.

What your feeling is a form of hallucination. If you were actually in WSP, you wouldn't be able to move anything. Possibly you just became super relaxed. But you have to remember, sleep comes in 4 stages, REM being the last in the cycle. Just be patient and keep that sensation, don't focus on it though because it may stop you from actually entering WSP.