M.P.
I suggest that this chang is OK. As he gets older he will continue to have changes. His body could be getting ready for a growth spurt or another physical change. It could also be that his therapy is working. Because he is active outdoors I think he is OK. I would ask about this at his next therapy appointment. My grandson's therapists have been helpful for us.
I don't think he is ill or gettiing ill based on your description. The medicAL field suggest only taking a child to see a doctor is when the child has a fever or when they are lethargic for more than a week. Your son's behaviour is not lethargic. He paticipates in life, only differently.
Isn't getting this sort of behaviour your goal? I'd embrace and nurture it.