Although he's been doing it for months now, especially when he was first learning to crawl, he would wake up crying on all fours, puzzled and upset why he was in such a position. I used to think he got himself there, but according to Moxie:

"All that physical development also makes it really tough for babies to sleep, and they often wake themselves up in the middle of the night with movement. It's a little funny when your baby wakes up and is shocked to be up on hands and knees rocking. His or her body just did it without any conscious effort."