This sounds so typical of night terrors, and all kids develop at different speeds, so he may just be getting to this a little early, our daughter did too, before age one, so it is not unheard of. If you see something else that you think is a medical problem, check it out, but this is probably not medical, my bet is that you are experiencing the developmental mystery that is "night terrors." Night terrors are not night mares, and have nothing to do with being scared, so you don't have to worry about this either, he is neither afraid or in pain, and he is not aware that it is happening at all, which is a very good thing!
We noticed more night terrors when ever our daugher was going through some kind of rappid growth or development, like learning to stand or walking alone. So if he is doing a lot of work all day on a skill, he may be more prone to them when that is going on, which just mean that he is making developmental progress.
The trouble is, no one can make this easier for his Mom! You really do just have to watch and make sure he does not hurt himself while it it going on. Try to reasure yourself that he is not in pain (pain wakes babies up!) and it will pass. One day in your future, he will have a day or night when you know he is in pain and you will be able to comfort him, you will know the difference so there is nothing for you to worry about, truly.