Well it could be something paranormal but i rather not go to that side that's more for the beyond dreaming section. The pain is quite interesting.. But maybe because u experienced it once in a lucid dream and was thinking a lot about it when u woke up, the pain and the person appeared again in your lucid dream cause u where thinking about it a lot?

I could be wrong, but at the moment this is the only thing i can think about that seems to make sense to me. Just try to keep your mind away from it, and if im correct it shouldn't appear anymore in your lucid dreams. U sayed "I WANTED to know what is it. I absorbed some strength and went to sleep again. " When u do this, ur kinda asking yourself for it to happen, if u can follow me on this one?

So just try to relax and think about other stuff, that's my biggest advice to you. It could be something paranormal don't get me wrong, but i think it's wise to just think away from that for a moment and look at the other options. Hope this helps u a little bit out.

Not sure if this is the answer u where looking for but i think it's just a normal lucid dream that went a little bit wrong. Once in a while something out of our control can appear in our lucid dream.