Sleep Smiles?

Okay, so my mom came in my room to wake me up for breakfast. This is how she goes about it.

She pokes me on my nose and says, "Sleepy-head, it's time to wake up." I mumble something unrecognizable and open my eyes. She is look at me a bit weird and smiling. She then says, "You must have been having a good dream because you were smiling in your sleep." She said it was SOOOO CUTE!

I'm not sure if I believe her. I thought only little babies smile in their sleep? I've looked around on the web and I can't find any information on adults smiling in their sleep or a solid reason while babies smile in their sleep. Reasons range (for babies) from dreaming of angels to having gas (I'm pretty sure neither was happening while I was asleep >_<) What do you think? You ever seen someone over three years old smile in their sleep?