Whatever the problem is, you're just going to have to see a doctor anyway. Here's a couple of common neck killers, though: stop turning your head to stare at yourself in the mirror (if you do that), if you are tall, stop pushing your head forward (rule out 'forward head posture'), keep your head in a neutral position while lifting (don't look up, don't look down). If you hear a tiny pop when the injury happens, then one of the tiny muscles in your neck may have gone weak. Flexibility training for your neck would be the best help, there.