T.G.
My 5 month old son, did the same thing at first. And I kept going back in there to put him on his side and give him his soothie back. But in a couple weeks, he learned to enjoy sleeping on his tummy, and that's how he sleeps now. I think that at first, they scare themselves with their new found skill, and then sometimes just want to practice it. Hopefully, this stage won't last long for you. Hang in there!