Rolled over or slid down?

Fer was lying in the MIDDLE of the queen sized mattress when I left the room to go attend to Kieran who was crying (he just woke up from his reluctantly-taken nap). When I returned to the room in less than 2 minutes later...

Anyway, as Kieran would say.. "fall down"... :P He somehow managed to slide off the mattress and landed nicely on his bum! He just sat there and waited. I didn't hear him cry or anything. In fact he even had a cheeky smile for me when I came into the room and saw him in that position! As I was getting the camera, he started sliding lower and lower. His head would have reached the ground if I were to leave him be for another minute! :P

It was funny, but now gotta start watching out for him and putting up all the bed rails...