Perfectly Natural, perfectly normal. Your body doesn't stop operating when you're unconscious, blood still flows, muscles move and chambers fill. Even if you're passed out you can still smell your wife and still feel her body next to you. When you're dreaming your mind processes thousands of ideas and images that you won't remember in the morning. It's pretty normal for guys to have "Morning wood". Tell your wife if she doesn't like you starting your day with an erection she's more than welcome to help you relieve that pressure.
I have the same problem and its really annoying. I dont sleep next to a female and like you I might be having a dream that has absolutely nothing to do with sex or intimacy. It's almost like clockwork, every morning when i wake up its erect and I have to lay there for about 10 minutes untill I get up to do anything. It's also really annoying when I wake up and its there but i want to continue sleeping. I have to wait for it to go away untill I can get comfortable again. What causes this?
havent you always woke with an erection, my 5 yr old son wakes with one, its why the joke of it being a kick stand, it keeps you from falling off the bed, it's just your body saying wake up and pee, your wife is insecure and worried about what you feel in your sleep?