The party wound down the way birthdays always did — cake going soft on the counter, balloons drooping by the door, your mom hugging you one last time and saying you'd gotten so big, so fast.You went to bed the way you always did, legs aching with that same familiar growing-pain throb you'd had for months. You figured it'd fade by morning, like it always did.It didn't fade. It spread — warm, strange, quiet — up through your hips and spine while you slept, like something rearranging itself carefully so it wouldn't wake you.When you opened your eyes the next morning, you expected the usual stiffness.You felt nothing at all.