In the worst cases diffuse RSI can develop into a chronic condition, as illustrated by the diagram below. A number of physiological and neurological dysfunctions combined with a loss of muscle tone and physical fitness can result in a seemingly permanent disability, one with some similarities to fibromyalgia.

The mechanisms behind this are, as yet, not well understood but it does appear that recovery and rehabilitation is still possible. (See here for one story of such recovery and the techniques used to achieve it).