Why does my neck hurt after roller skating?!

Your neck muscles are tight. They could have tightened up because of the fall or by just how you had to try to balance yourself. Freeing up your neck muscles will get rid of the pain for you and here's how to do that:
Neck
Put your hands alongside your head so your thumbs are on the front of the muscle under your ear and your fingers are on the back of the muscle behind your neck. Squeeze your thumb and fingers together and hold. Relax your body. When your fingers and thumb touch, about one minute, slowly lower your head as far as you can, release the pressure but hold your neck lowered for another 30 seconds.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.