The first thing you're aware of is how sore you feel. You open your eyes and see the grove surrounding the pond, brightly lit by the morning sun. You remember what happened last night, how you got lost in the maze and fell into this pool, passing out from exhaustion. "Wait, why didn't I drown?" you wonder. Falling asleep in water is usually lethal, but you're alive. You try to turn around by your torso won't move. Turning your head to look, you realize that some vines have reached down from the branches above and wrapped themselves around your chest, holding you upright.
You also notice that the water has grown warmer and the feeling has returned to your body. You can now feel the thick vines wrapped across your bare skin. Wait, bare skin? You fell in the pond fully clothed, where did your shirt go?
You look down to see the tattered remnants of your shirt floating around your abdomen, but that doesn't concern you anymore. Your bare chest is covered with a curly layer of hair, but you can see the powerful muscles underneath. You look at your arms to see them similarly changed. You look at your reflection and see that a thick beard sits on your face, your ears have also become pointed.
Frightened, you realize that you can move, and so you finally leave the pond, breaking through the vines. As you walk onto land at last, you feel more mass than normal leave the water. Standing on the grassy floor of the grove, you look back and see the hindquarters of a horse. Looking down you see the front hooves of a horse where your feet would be. You bend forward until you're looking behind you at the rear legs of of a horse, with a very equine set of genitals between them.
You're a centaur now, and still lost in a hedge maze.