Freaking out please help

ladylamb

For some reason glow won’t let me upload the video, but my son keeps doing this strange tremble thing where he stretches out his arms and legs, goes stiff, and makes these weird “ah ah ah” sounds. They last a second then he goes back to laughing. I don’t know if I should take him to the doctor or not. What’s going on? It only started happening today, he is 14w4d old.