This is such an interesting perspective on ghosts and their prevalence in history across the world. Reoccurring violent dreams or anxiety and fear in the middle of the night from PTSD would make sense.
I dunno, epileptic seizures were "demons", cancer would be a "demon", so ghosts of slain warriors could certainly be thought of a "demon" as well? You would have to ask that Sumerian Healer though: I wasn't there, so cannot speak for them:-).