It may men you guys had a fight and just went a little over board when you were sleeping
What does it mean when you dream about beating up your current girlfriend?
Dreams, most of the time, do mean something,Maybe you went to bed angry and she was in your dream, so you took your anger out on her?Maybe it was a nightmare and you love her so much it'd be horrible for you to see yourself do it to her?
It doesn't mean any thing just mean you imagined in your dream just make sure you don't do it to her in real life.
Maybe things in the relationship are not all that good