need help understanding my SP experience

Okay im pretty new to all of this so bare with me here... Okay so i have researched this and im mainly finding out that when a person does experience this they can not move their whole body and they're stuck there feeling something heavy on their chest, but what happened to me is i saw this greyish figure walk in front of my bed i couldn't tell if it was male or female. I didn't know what was going on so naturally i freaked out. At first i couldn't move but once i started panicking i could move my upper body but not my legs i was trying to get up and fight whatever was there. I could hear it laughing and making fun of me about how i was trying to yell and fight. Then all of a sudden i tried calming down but i woke up sweating and breathing really heavy. I just wanna know why i could move my upper part of my body and not my legs. Im not too concerned about the greyish figure cause i will try and deal with that as soon as i figure out how to use my legs.

Just another question why is it that every experience i have read about has one "being" that everyone sees? Is it there to see if we are ready to lucid dream by making us fight and overcome our fears first before we can do anything?

I'd guess you moved the upper part of your dream body, not your physical body. Probably only partially separated or whatever they call it when you're still getting signals in from the physical body. When you woke up for real, were you sitting upright, or laying down?

I think most of your experience was not sleep paralysis but rather a dream about sleep paralysis. If you are unfamiliar or anxious about what SP feels like, this can carry over into the dream and create the sensations and imagery that you experienced. This is just your mind filling in the gaps of unfamiliar territory.

I've also had it happen where I was in a dream where I was sucked into a scary entity, and woke up paralyzed. My fear and struggle led to me slowly waking up, and I do seem to remember it first came as little twitches of my torso.

I used to experience episodes of Sleep Paralysis on a regular basis, although they are few and far between now. I don't think they are anything to worry about at all, although people understandably freak out the first few times it happens.

I believe (forgive me if I'm mistaken) that it occurs when the paralysing mechanism which prevents us from acting out our dreams fails to switch off immediately after awakening. The hallucinations are the result of dream imagery overlapping with images from the real world, normally taking on a frightening appearance because the brain enters a state of hyper-awareness due to the vulnerability felt as a result of being unable to move.

I have had hallucinations of demonic hooded creatures, evil witches' faces and even tiny little demons crawling over my body :S. Now, when I have an episode, I don't see anything at all, because I am aware of being paralysed and simply let it pass.