Thanks for choosing HCM.
Your symptoms , to me , point towards a spasm in cervical spine[neck],leading to cervical spondylosis
Try the following-
1] Hot fomentation to the neck on the back side.
2] Mild cervical [neck] movements / exercises.
3] Apply any pain reliever gel to the back of the neck & take some pain killer tablets containing muscle relaxants.
If no improvement get a X-ray / MRI
of the cervical spine & report back.