Reminds me of the little girl who had a little curl. When she was good, she was very, very good and when she was bad, she was horrid. Don't want to worry you, but this sounds like the behaviour of my DGS1, who has just recently been diagnosed with Aspergers syndrome. He was charming and very bright at nursery school, but different again at home. He has nipped and hit me and has even tried to bite me when he has a meltdown. Soon as it is over, and he has gained control, he is his lovely little self again.
All I can suggest is "wait and see". It may be just a case of the "terrible twos".
Things you learn from Watching TV (light hearted)
Disappearing contributors - part 2

