Much of neck pain is actually muscle pain. When you moved the neck, you relaxed the muscle some, and so when you repeated the movement it didn't hurt. But neck pain also usually comes with some pressure on the nerves as well as on the muscles and so the pain can move around. When you say overexertion, exactly what did you do? If you strained some muscles, they take as long as they take to heal. Long for some, quick for others. Quick for young people, longer for older folks. If you caused an injury and not just a strain, longer, as the injury must heal. Sometimes, if you don't get the inflammation out quickly enough, it can become chronic, and then you like me get old with a chronically sore neck, which I'm sure you've seen many older folks have from things they did when they were young. Peace.