You can feel your bones shifting underneath your skin. The feeling is very uncomfortable, and slowly gives rise to a dull pain in your back. Fortunately, the bloated feeling has passed, but at he pain in your back gets worse, you'd rather it stayed.
You think its probably a good idea to tell Nurse Redheart about your new found back pain. As you start to get out of the bed, a bone on your back jerks to the side sending a wave of intense pain though your entire body. Your body spasms and you fall down onto the floor. You manage to roll onto your stomach, you try to get up, but your upper back erupts, it feels like its on fire.
You can't even move, you can only feel more bones shifting and even more pain. You wish somepony would come by and put you out of your misery, you close you eyes and hope it all ends soon. You must have blacked out at some point, because when you open your eyes Nurse Redheart is there, lying beside you, your head in her hooves. She's saying something, probably trying to comfort you, but you can't hear anything.
Soon you feel the skin on your back stretch, and then in two separate places, split open. Something begins to force its way out of each hole. The pain is almost immediately gone, and you start to think clearly again, the first thing you hear is nurse Redheart's voice.
"Oh, dear Celestia." she manages. Probably not a good sign you think. You decide to take a look at just what forced its way out of your back, and it only takes a glance over your shoulder to reveal the answer: You've grown wings!
Your wings are about the same size an any pegasus pony, They're orange, much like your coat, and they are also covered in your blood, you guess that when they split open your skin you must have bled all over them. Your body also feels much lighter, but you don't know why.
With the roaring pain of your transformation dumbed down to just a dull whisper, you give your wings an experimental flap, they seem.... awkward.
Nurse Redheart finds her voice again. "I can why I missed this in the tests. I've never had a pony grow wings before. Sorry but this is quite fascinating." She pauses for a moment. "I think I'm going to have to run a few more tests! Please, stay here while I get them ready." Redheart hurries off, no doubt gathering up what she need for the next round.
You sit up on your rear, admiring you new wings, you wonder if you'll be able to fly on them. You look to the door of your room, and for the first time since the beginning of your ordeal, you begin to relax, when.....