Adopted Unneutered Adult cat into a 6 cat home, all fixed. No aggression towards other pets, so why towards me randomly?

He has had a rough few months of bouncing between being left outside and getting beat up by something, and being thrown into a dark dirty basement for isolation. When I took him he was affectionate, sweet, attention hungry. He has shown zero aggression through doors and screen doors towards my other pets. I slept in his room on night one. I got out of bed to shut the window and then went to get back into bed, he attacked, grabbed onto my back with all claws. He stopped quickly and sat there. I went to pet him and he grabbed my arm and bit hard. I turned my back to him and slowly lowered into bed. A few min. later he came up to me purring and rubbing on me, so I pet him again, only to be attacked again. Left the room that time! The next morning he was fine, and that night went so well I was able to cut his nails, but the next morning I was again attacked. Any ideas what this sounds more like; Behavioral, hormonal, or stress?? Will neutering him help if he's an adult and it's hormonal??

Asked by Member 1109045 on May 3rd 2012 in Aggression