Against your better judgement, you step into the ring of mushrooms and lie down for a nap. The grass looks so soft and inviting, and you are feeling pretty groggy...a little sleep will clear your head, and then you can find your way out of the forest. Besides, there aren't any animal tracks in the ground, or any scat or anything, so probably nothing comes here very often, and it's a state park anyway, so there shouldn't be any dangerous animals in the area, right? You should be safe enough. These comforting thoughts in your head, you lie down on the soft grass, stretch out, and go to sleep.
When you wake from peaceful, dreamless sleep, it's dark out, except for the stars and the brilliant full moon overhead. Judging by its position, it's probably somewhere around one or two o'clock in the morning; you must've been a lot more tired than you thought! But something seems wrong; the trees seem a lot farther overhead than they were when you went to sleep. Moreover, there's something heavy on your chest, and you feel the wind over your bare skin. Where are your clothes? You sit up...
And it's immediately apparent that something's way wrong. That weight on your chest is your chest; you can feel it...no, it's two weights, and you can feel them bobbing around as you sit up. You're instantly wide awake, and although you're afraid of what you're going to see, you force yourself to look down. It's exactly what you feared; hanging from your chest are two female breasts. Below them you can see two shapely legs, nestled between which is a private area that is definitely not male. Long golden hair hangs down into your field of view, and you realize that somehow, during your nap, you became a girl. You gasp in shock and horror, revealing a changed voice as well, soft and high-pitched.
Your mind reeling from the surprise, you almost don't notice that you're sitting on...fabric? Yes, although you're completely unclothed, you're sitting on cloth. Looking down towards your dainty feet, you see an oversized shirt collar. A suspicion forming in your mind, you look around...sure enough, you're sitting in the neck of your T-shirt, which is lying on the ground in about the same position as you were. Further down are your pants, socks, and shoes. Not only have you become a girl, you've shrunk as well; you can't be more than four inches tall. You stand up, and notice your shadow on the fabric of your shirt; while it's unsurprisingly the outline of a shapely young woman, there are four lighter shadows surrounding it, shaped like...wings?
You turn your head, craning your neck for a look back at yourself. There are indeed delicate, translucent dragonfly-like wings sprouting from your back; you can feel them connect around the base of your shoulderblades. Almost without thinking about it, you move them slightly, feeling the muscles move like any other part of your body, watching them flit from position to position. You look around you at the circle of mushrooms, and remember reading once that these used to be called "fairy rings." It seems quite appropriate now, given that you went to sleep in one and woke up as a fairy.