well perhaps the enzymes don't operate when you sleep to make you hungry. like your smell is not working either when you are alseep.
Yes, your sensory input is down. But you can still imagine it - thus, you can't see when you are asleep, but you surely imagine images. So why can't you imagine hunger?
I saw on the TV sometime back that there are people who sleep eat like sleep walk. so it must be possible. glad I dnt ahve it though trying to keep the weight under control that would just make it worse!