Rare statistically, but since you're a lucid dreamer (you lucky bastard!
) it is hardly surprising.
It's physiological phenomenon, simply an extension of your lucid dreaming: your mind awakes, but the rest of your body is still asleep. When your brain sends signals to muscles, the other parts of the brain responsible for managing you while you're asleep go 'HELL NAW!' - and they have a good reason. If we didn't have that part, if you dreamed you were, say, walking, you could stand up and walk straight off your bed, in the cold, unwelcoming embrace of the floor.
You can move your eyes, since eyes have a hotline to the brain - similarly to people with Locked-in Syndrome.
The scary shit you are seeing is you dreaming while awake. If you lived in the 50's to 70's, you'd probably be seeing little green men.
'What do' part: uneducated guess, but I assume getting rid of the lucid dreaming would get you rid of Sleep Paralysis, since it's the same kind of brain activity getting mixed up. The parts of brain that are normally shut down while you're asleep aren't, leading to lucid dreaming, but the parts that are supposed to shut the hell up while you're awake are neither, leading to Sleep Paralysis and general freakishness.
What might potentially help: look up what to do to experience lucid dreams, then do the exact opposite. That's assuming the techniques people are giving actually work, and that in their absence you can stop LD.
Second, but that's really not a good idea, especially in the long run: alcohol. Shuts parts of the brain off. That's what being drunk is, basically - having certain parts of your brain shut down biochemically. If this would work, I have no idea. Theoretically, it might, practically, probably not.