Pain and stiffness in your shoulder can make every activity, including sleep, difficult. Worsening shoulder pain, especially at night, could mean you have a frozen shoulder, says Dr. Christopher Camp, a Mayo Clinic orthopedic surgeon.
He says frozen shoulder happens when the lining that goes around the shoulder joint gets inflamed, possibly the result of a small injury. It thickens over time, forming scar tissue.
Source: Medical Xpress