You may have developed cervical dystonia (othewise known as spasmodic torticollis). Dystonia produces sustained involuntary spasms of certain neck muscles, usually on one side, and deeper muscles can be involved (the spasms usually only subside in deep sleep). You would need to a doctor (usually neurologist) who specialises in diagnosis and treatment of movement disorders to determine this and what may be done to improve your condition.
Cervical dystonia is often treated with regular (usually 3 monthly) Botox injections to the affected muscles, which weakens them.
If your condition continues, and physical therapy is of no benefit, and scans do not reveal any underlying bone or nerve problems, then it may be worth seeing a movement disorder specialist for assessment.
I think you have soft tissue injury in the neck. A lot of alternative medicine can help.Suggest acupuncture and chiro......