Well, usually when attempting a WILD, people tend to feel their body either float up off the bed or fall through the bed, and that signifies when the have entered sleep paralysis and are on the verge of a lucid dream. I don't think, however, a falling feeling like that would signify sleep paralysis, because that falling feeling normally would wake a person up, like what happened to you. I could be wrong though so don't hold me to it. I do however know that when you are falling in your dreams it usually happens when you are under large amounts of stress, feeling overwhelmed in your waking life, or a certain sense of failure or inferiority.
The mind is a beautiful thing