Sitting up & crawling

Baby J has started sitting up on his own about a week ago!  He starts from a prone position and then pushes off with his hands to sit up.  Since he managed to master it a week back, he's been constantly in a sitting position, and gets upset with you if you leave him in a lying down position.  It's pretty scary sometimes cos I can wake up in the middle of the night when he cries to find him sitting up in his cot.  He also topples over pretty frequently, so we have to leave him in the travel crib to play instead of his cot otherwise he always bangs his head on the cot.

He's still trying to master crawling though.  He can only bulldoze forward with his head down and little nose smushed on the mat.  With him so active, I really have my hands full when he's awake!