Hi. My 10week old has always done this - in the day as well as night so Ihave been able to observe her and realise she is not awake. I have tried using towels folded to support her on either side (lower than her head) as she does this - have to put them besides her very carefully as she wakes easily. She does push them to the side eventually but I find it gives support for just a few moments - long enough for her to drop off properly again. I take it your little one is a fidget bottom like mine? ALWAYS moving around- Izzy does a 180 on the changing mat now using her legs!