Cramps and jitters 12mo

My baby is just over 12months and the past three weeks he's been...shaking uncontrollably for 1-3 seconds a few times a day.

It happens mainly while eating or drinking, for example he will bite down on his bottle, his jaws will clench, his body goes stiff and shakes/jitters for 1-3 seconds.

It has happened while we were playing too, when he was not engaging his mouth.

I have filmed it with the camera but each episode is very brief, but it happens a few times a day.

When i hold him i can feel his body tense up and shake/jitter. It's almost like a spasm?

Has anyone else experienced this?

He is otherwise healthy and happy. I'm seeing the nurse next week.