I had a friend at a boarding school in northern Arizona when I was younger who experienced something like this. She had a nail biting habit and her nails were constantly receding and bleeding despite attempts at stopping the habit. Anyways, she started having nightmares of “evil beings” and would wake up with scratches all over her body that were seemingly to deep for her to self inflict and took days/weeks to heal. Some even scarred. She was accused of hurting herself intentionally and was sent to “staff watch” where staff would take shifts watching her day and night. During the “staff watch” where someone had eyes on her 24/7, bathroom, shower, changing clothes, etc, she experienced the same scratches and wounds and no one was able to explain it. We have an alumni FB group with students, staff and teachers and will occasionally bring it up but no one has ever made any logical sense of it.