Very interesting. A couple of times I've had similar sensations, a strong pull upon forced separations... but I felt it at the opposite side of my body. I always thought its the "spleen chakra," the only center that's pictured excentrically in some esoteric systems, such as theosophy. Now I think this chakra is the external component of a center located in the right temporal lobe, including the memory center, hippocampus. So in your case these sensations might signify a small loci of seizure in your left temporal lobe which comes into life during sleep paralysis.