Rotator cuff tear
The rotator cuff is a large group of muscles controlling movement at the shoulder. A torn rotator cuff is most common in people over 40. Most people don't remember hurting themselves beforehand.
If you have a torn rotator cuff you may find you have pain and can't raise your arm properly, especially above shoulder height. It isn't always painful, although some people have pain for a few weeks before they notice any difficulty with movement. Symptoms can be similar to painful arc (or impingement) syndrome and tendon tears are often found after an ultrasound or MRI scan.
The neck and shoulder muscles can over-compensate for lack of movement in the shoulder causing hunching of the shoulder which can lead to neck pain.
Physiotherapy is often helpful, but surgery is sometimes needed to repair the torn part of the rotator cuff.