This is a risky thing to do, be careful.
I once did this and 'thought' my MBP was asleep. Luckily I had left my backpack zipper open a little and heard a weird, high pitched wining sound. At first I had no idea where it was coming from then I realized it was from my backpack, yikes! I pulled out my laptop and it was screaming hot! Almost too hot to touch!! The fans were going full blast. I opened the lid to help with air movement and as the minutes went by it was still super hot and the fans were still screaming. So I opened the refrigerator door and held in inside. Soon the fans started to slow down, the casing felt cooler and it went back to it's normal, quiet and cool self.
I know there's been many posts about MBP's getting 'a little' hot and things like graphics cards failing but man I'll tell you, I'm seriously impressed that my stupid mistake didn't kill this thing. Rock on Apple!