I read an article about a two year old who just went quiet one day, and completely stopped responding to his mother...
Poor parents were frantic he had gone deaf and had him in and out of doctors rooms for a month if I'm not mistaken.
Turns out he was just ignoring his mother.
He probably found her quite annoying to ignore her for so long...
I agree with Lolagrace, let the child sleep, the doctor clearly isn't worried, so I don't see a reason to panic.
Maybe the poor child is protesting being awake.