J.-
I'm with those that say developmental. Many babies try to "practice" their new found movement in their sleep. It often wakes them and usually wakes us.
The other possibility is teething.
I also had the silent reflux with my daughter and she adjusted her eating habits so she would only take in about 2 oz at a time, day or night, to keep the reflux at bay. But, it doesn't sound like your little guy has reflux, but just in case, try adding a baby friendly probiotic to his bottle. Just one dose a day is sufficient and if he is having any trouble, it will make a huge impact. If he isn't having any trouble, it won't hurt him and it will just make his digestive system that much healthier.
I do believe that this is a phase and he will move past it when he has mastered whatever it is he is practicing. Of course, there will be other phases that do this again...
Enjoy every moment, they don't last long and they are on to something new.
D.