nightmare (from luu, bone and painama, to haunt)
This is the opposite of unenägu, another interesting word. Some dictionaries translate this word as Incubus or Succubus, both of them, non pleasant mythological characters that would come in one’s sleep. Painama, however, can be translated also as to haunt or to obsess, the basic concept of stalking. Based on this, I’d say that luupainaja could mean “stalker of the bone“, which would perfectly illustrate this concept.
I just hope that doesn’t happen to me tonight.