S.O.
If it is at the same time everyday it might be a noise. Does a train go by or does someone start their car for work? It could be all the things everyone else said too. Ears, pain, bad dream. Night terrors were when my son was younger. Now that he is 2 1/2 he can tell me he was scared or what was happening in his dream. (he doesn't know it was just a dream, to him it was real. That's why he is so scared) sometimes he even remembers them the next day.
Did anything else change recently? Move to a different house? Meet new people? Rearranged his room? New family member? These things might contribute.
Hope he sleeps thru the night soon.
S.