Oh something else i thought of.
DS does something DD didn't. As well as the thrashing/kicking/hitting he actually gets out of bed and has had some nasty collisions with DDs bed/desk if I'm not quick enough to get in there and guard the end of the bed (while I try not to touch him it's great fun - not). I've found him in random corners of the house when I was busy doing something as he started, facing into the corner, not awake, screaming.