I was messing with my Nokia Lumia 520's settings late at night and I accidentally turned off the vibration. It's great and all but not for me. The thing is, I can't figure out how to turn it back on.
Press on one of your volume keys as if you're adjusting the volume. You'll see the white downward-facing store in the upper-right corner. Tap that and your full volume controls will appear. You'll see the vibrate toggle at the bottom of this section, just tap it to turn your vibration back on.