We went through this with our son. Some children internalize anxiety and may not even realize they are anxious. Our pediatrician suggested we give him melatonin before bed. It works wonders.
Has anything different happened in his life, new home, new sibling, new school are you working longer hours if you work , very often if a routine gets disturbed children get a bit upset .,has he been away from home.Unless you wnat him to the best way is to tell him he can come into your bed for a while when he wakes up or at the weekends, that way you are not setting up a president .Maybe he just wants a few more hugs ..good luck