Can be from contact sport, injuries, head knocks.
Your chosen musculoskeletal expert, physio or chiro will run a few tests to assess movement and function of the neck. Test grip strength, muscle strength, nerve function. Sometimes xrays and MRI’s are warranted done the track if the patient is unresponsive to conservative management.
It depends on several factors. How chronic it is, expertise of practitioner, compliance of the patient to home advice, stress in patients life just to name a few.