Nocturnal seizures?

So for the past 2 years me and my husband have lived together, once a month I guess he will wake me up shaking, almost like a seizure but as soon as I say his name or touch him he says what? Wondering what I'm doing. He says he never knows when he's shaking but when I wake him it's like he was awake and barely asleep and I know he's been sleeping. Can someone please tell me something, relate, or give an answer? I'm worried