My ds is 16mts and usually sleeps through until 5 ish. THen the only way he will go back to sleep is if i put a dummy in. I have tried to leave him, but he just ends completly waking himself up through shouting. He doesn't really need a dummy any other times unless hes very upset. How can I get him to re train himself to get himself back to sleep at 5am rather than want to get up???