Hi,
That is very odd. This may be an odd response from this website since it is about medical opinions from everyone in the known universe but I am suggesting that you reach out to a spiritual healer/psychic medium to find out if something is causing this to happen to him. If you find out that there is no spiritual influence, then it's all medical.
There's no harm in that.
Being that he is such a young child, that does not sound right to me. I truly believe something spiritual is happening to him and he needs help there.