A slipped neck disc occurs when some of the soft tissue that separates the vertebrae bulges out towards the spinal cord in the cervical area.
While this may push against the spinal cord or the nerve roots and cause pain, it is also possible to have a slipped disc and not even know it - it is estimated that up to 20% of the population have slipped discs without experiencing any noticeable symptoms.
The most common cause of a slipped neck disc is age, although they are occasionally seen as a result of trauma such as a fall or whiplash from a traffic accident. Slipped neck discs are most often seen in those between the ages of 40 and 60.
As noted, it's possible to be symptom free. However, most people will experience localised or radiating pain, or some muscle spasm or paralysis.
Treatment is usually conservative, with surgery only used when other approaches have failed. Physiotherapy and exercise, with an appropriate program of painkilling medication, can relieve the symptoms for many people.
The exception of course is cases involving serious or increasing paralysis, which are treated as emergency and which require immediate hospitalization.