You are having a realy strange dream. In this dream, you are a large, shaggy jackass, and you are mounting a beautiful young quarterhorse. Your huge penis throbs, your enormous balls pulse, and you bray in pleasure as you send your seed deep into her womb to make a new mule.
Except - this dream is awfully real. You can feel the pleasure, but also the sweat and pressure, the stink of manure and the odors of the mare and your own musk. You can feel the dream penis getting softer, and you slide off onto four hooves, panting from exertion. A deep satisfaction fills your mind, a primal need has been filled.
You are not waking up yet. In fact, you feel more awake and alive than you can ever remember. Flies are buzzing around your muzzle, crawling on your still-erect penis. Slowly, more slowly than you should, you realize that this is all real. You are a jackass. And you just fucked a horse.
The thought doesn't bother you. Nothing bothers you. Something has happened to your brain - you remember being human, but now that you have discovered you are a jackass, well, that is OK too. It is not bad - just different.