Doubting psychosis

My wife and I have been having issues with respect to my sister. I am wanted not giving details about this issue. This issue went out of hands and when I don't agree with my wife about my sister, she starts hitting herself on the head like a maniac. She also once started hitting her head and kicking her legs like she was possessed. I've not faced things like this in my life and I don't feel I deserve this behavior of hers. Is this a psychosis symptom?