My baby has just turned 7 months, he has previously always gone to sleep in his cot fairly easily at bedtime and for naps in the day. Now he has suddenly learnt how to sit up and he refuses to stay lying down in his cot - he pulls himself to sitting and starts bouncing about - inevitably then bumping his head on the side of the cot. It's taken 2 hours to get him to sleep tonight - it's driving me insane!! Would be very grateful for any advice??