My 10 month old DS first started doing this several months ago but then stopped so i actually forgot about it but over last couple of weeks its started again.

He clenches his jaw and fists and then his whole body shakes like its vibrating (i dont know how else to explain it). It lasts for about 10-15 seconds each time. It seems to happen more often when he's in his highchair but happens other times as well.

Im starting to get a bit scared as its happening more often now. I just fed him and he did it about 10 times in 15 minutes.

Is this normal behaviour? Should i be taking him to the doctors for it? Has anyone else's bub done this?