Thanks for your replies ladies. I've been watching him over the last few days and it seems to be happening when he's tired (which unfortunately is all the time ATM as he's only sleeping for 15 mins during the day - but that's a whole other thread!!) and frustrated. He's just so incredibly wilful though - yesterday he started hitting his head against the back of the high chair because he could see the nurofen and I wouldn't give it to him!!! He doesn't display any other worrying behaviours (and I've checked the fridge/pantry thanks Shades!) so I'm just trying to ignore it as best as I can...

Thanks again