This is how I found Silas when I came back into the room on Monday morning. He was on his back when I left him... :)
Now he will hardly stay on his back! He also figured out how to roll while swaddled, so we had to stop swaddling him and he was not very happy about that for a couple of nights. Now he's good with it because he just rolls to his tummy, cries for a minute or two, and then settles in for some good sleep in his new sleep sack. We are working on teaching him to roll from his tummy to his back, and he did it all by himself this afternoon so yay!
He is definitely an active sleeper. I love this picture - he started out with his head facing the right and in his stabilizer and this is how I found him when I went to get him up. :) He was awake, not sleeping with his face in the mattress.