The term frozen shoulder describes the gradual process of inflammation and adhesion that occurs within the shoulder joint. Sometimes this occurs for no reason, sometimes after a fall or other mild trauma such as lifting at arms length or at an awkward angle.
The healthy shoulder joint has a large available range of movement and this requires the internal capsule of the joint to be quite loose. In this process the inflammation tends to collect in the loose folds of the capsule, especially at night when the joint is still. It is sometimes the case that the joint affected is the one that you like to lie on at night and this usually becomes difficult then too painful as the condition progresses. This often causes loss of sleep.