Wrong posture can increase the weight of head on the neck by a few kgs. Poor neck posture can lead to head moving forward which is one of the most common causes of neck, head and shoulder tension and pain. The resultant extra weight/pressure leads to flattening of the normal curve of the cervical spine resulting in abnormal strain of muscles, ligaments, bones and joints of the neck that causes joints to deteriorate much faster than in normal case that finally causes degenerative joint disease or neck arthritis.
As shown in the diagram attached, for every inch that the head moves forward in posture, it increases the weight of the head on the neck by 4-5 kgs!
Try out these simple wall tests to find out if your neck/shoulders have already deteriorated