You pulled back on the leash. Sure, you were much larger and stronger than your former human frame, but that blasted bridle gave him more leverage. He could twist it around to make your head at odd angles. You headed back towards the driveway little by little in this tug-of-war. Eventually, you got an idea. Instead of pulling back, you could suddenly charge him.
Digging all four hooves into the grass near the driveway, you suddenly charge forward. The imposter gained a fearful, surprise look on his face, as he immediately started flying backwards. You put your head down, and laid his flat while he was already falling. He landed on his back on the hard driveway surface, as you charged through him.
Triumphant, you circled around to confront him. But he was lying on his back, oddly twitching. His entire body was twitching. Worried, you came over, and could clearly make out the vacant, staring expression of his eyes, despite your own poor eyesight. With horror, you realized he looked like he was dead or dying! His body was convulsing as he was staring at nothing.
You then smelled the distinct iron smell of blood with your enhanced donkey sense of smell. You started hyperventilating. Braying the only irritating noise allowed to your new species. You see a dark stain pooling around your former head, as it started streaming down the driveway. All you could do, is stand there braying at the horrendous scene before you. You just...killed yourself!
You heard a scream from inside the house! You heard your wife screaming your name! A feverish fear gripped your entire being. You black out, as your body's donkey instincts for fight or flight took over. Your new body ran turned tail, lowered it's ears, and ran. And ran. And ran.
Eventually, you "came to." You had no idea where you were, nor had any recollection of how you got there. All you know, is that you were staring down the long snout of your donkey face, with it buried in a field of grass, munching on the yummy substance. You tried pulling your face away, but your body's instincts were still too strong and your mental state and well-being way too weak. Much to your growing horror, you began to feel like you no longer had control over your body. And indeed, you do not.
You spend hours grazing out in this field. You slowly come to recognize it. It's the field that you came from! Somehow, you made it back! This was the donkey's home. You wanted to bray. You wanted to bolt. But you couldn't. You did not have an ounce of control over this body.
Little did you know, that when you killed your former body, that donkey's "spirit" entered its own natural body. Through the magic of the ring since your body is now dead, it has sealed you inside the same body. You did not technically die when your body did, and so, there was nowhere else for you to go. And because this wasn't your body, you don't get any control over it at all. The donkey retook it's rightful place in the universe, and with it's former low-level donkey intelligence. From now on, you're just going to be along for the ride.