What Causes Itchy Scratches On Back And Arms?

I have unexplained scratches on my back and arms when I wake up in the morning. They can be itchy so when I scratch them they will bleed. I have had them before and then they disappeared for awhile and just came back. I know they can't be self-inflicted because they are in a spot on my back where I can't reach. I have read some bizarre things on the internet about paranormal happenings causing people to get these scratches. I avidly change my bed sheets and definitely am a clean freak when it comes to taking showers. I do have cats who will jump on the bed, but I am really puzzled what causes these scratches.