I have a 4-year-old boy on the autism spectrum. It's the same story with him.
He has two modes: He is either hyper, physically hitting, babbling, and screaming, or he is hyper-concentrated, quiet, intelligent, affectionate, and sweet. My 3-year-old is starting to copy everything.
I loved the article! I need to stop beating myself up about slacking in certain areas because just getting through the day with my sanity right now is an accomplishment.