He's not done it till this week. I put him on his back for a nappy change and he seems to be ambushed by the startle response, and flings his arms and legs out looking really scared.
He's done it loads since about a week ago. I normally settle him by placing my hand on his tummy but he still looks perplexed and worried till it's all over and he's upright again.
Any ideas what's causing this?