The stock answer for this around these parts, is that’s probably a parasite trying to get a free lunch, and to banish and cleanse.
When banishing doesn’t work, as it sounds in this case it would just wait at a distance and ten try again, I would deliberately go back into the dream state and attack it, trying to kill it. Usually with fire. It will probably be fine but learn to leave you alone. Attack is the best form of defense type thing. 
What’s more, other entities will know what happened and also not start with you, knowing what happened to the other. At least that’s worked out that way for me.
We have a few discussions about parasites on here and some tutorials collected here in case that’s helpful: