Dreams about arguing with my dead mother?

My mother died just under 9 years ago from MS (Multiple Sclerosis). About 2 months after she died, I had several dreams that she was alive and well again. I would hug her and say, 'I can't believe you're here, I have so much to tell you.' I knew in my dream that she had 'gone away' but didn't know where she had gone and I was relieved to have her back and see her walking again. Lately, the dreams I've been having are my mum and me having really big arguments. We yell and scream at each other, walk out on each other and don't resolve the argument. However, I don't know what it is that we argue about. All I can remember is that we yell at each other, say what we want to say and then the dream finishes. These dreams are disturbing as my mum and I never screamed at each other when she was alive. We did fight and argue but never screamed or yelled at each other. I'm wondering why after 9 years, all of a sudden, these dreams are happening?