When we dream while we are asleep, our brains are in an altered state. Some of our senses are totally or partly dormant, our eyes perhaps most of all. And I think most of us do not remember most of our dreams, although some people may report otherwise. I don't know if neuroscientists have monitored activities in people's hippocampi during sleep, by I hypothesize that our hippocampus is less active or differently cative during sleep, including dream sleep, than when we are awake. But I wouldn't conclude that that, or dreaming itself, supports the idea of dualism.