My first ds had night tremors from 9 months too, it is extremely common in boys.
We took Nick to the dr as dp and i were very worried about him, the dr told us that when he is going through it do not wake him!!! It can make it a whole lot worse.
We were told just to watch to make sure he doesn't hurt himself.
When the terror was over Nick used to just lie back down and go back to sleep and he had no recollection of having them.
It lasted until he was around 2,and they just stopped.
I hope this helps