ok i am having this problem with my neck locking up on me and its not the joints at all,its the muscles that s the problem.I been going through this for a long time sense i was 23 years of age!Its like if i move the wrong way it locks up on me or when i am working out or just dancing.I have really no pain when this happens.when it happens its like dealing with nerves/pain!My mother had the same problem, and she had it real bad to the point it looks like some one is pulling at her muscles, and her head would get stuck one way, or it will move by it self.I have not got to that point, but every day its getting to be like hers. Need help pleas!
First, you should go to rheumatologist. Do lab investigation like ionized and non ionized calcium, thyroid function tests like T3, T4, TSH. Ultrasound should also be done to exclude any swelling in neck. You should take muscle relaxant oral Chat Doctor.  Being sportive person is good side on your case. I hope to follow your case.