M.O.
My pediatrician told me that it was not unusual for a child to still have night accidents until they are 6 or 7 yrs old.
He might be going through a growth spurt or had some kind of change recently that could be affecting him. Also at around 2.5 yrs their imagination really starts to take a hold and he might be dreaming a lot more causing him to not feel the "I have to go" feeling.
Trying taking him to the potty before you call it a night. Getting him used to waking to go to the potty might help. But I wouldn't be too concerned. He is still young.