"What's come over you?" means "Why are you acting so unusually?" The idea of "(something) coming over (someone)" refers to an overpowering feeling or possession. You are affected by something beyond your normal control. eg. "As I listened to her sing, a strange feeling came over me." The addition of "here" just gives immediacy to the phrase. You are demanding a reason for the person's strange behaviour.

What's come over you? = what is wrong/why are you so upset?