The most common cause of neck pain in young adults these days is excessive use of computers and mobile phones in the wrong posture. Prolonged sitting with the neck bent forward causes a lot of stress on neck muscles. This causes muscle spasms, stiffness, and pain. If the pain radiates along the arm, it indicates pressure on nerves.
The treatment for this is proper posture, taking frequent breaks while working on computers, and doing stretching and strengthening exercises of neck muscles. If there is numbness of hands or weakness, then one should consult an orthopedic doctor.