I allow my two chihuahuas to also sleep in my bed with me. I swear, no matter the size of the bed, they will always sleep as close to me or on top of me as possible. I think it has something to do with body warmth. With my dogs, they love to cuddle and have human contact. They love to sleep between me and my boyfriend and they feel extremely warm when they curl up around us. So whether I fall asleep on the couch or on the bed, they will always crawl in to sleep with me.