When the Hypermobility Syndrome was first put on the medical map in 1967, it was defined as the presence of musculoskeletal symptoms (predominantly pain) occurring in otherwise healthy individuals. Thirty years down the line we now think that there are probably two types of hypermobility.

The first is a milder type occurring in people whose joints are just like everyone else's but which have the capacity to move more than most people's joints. The other, a more marked form, has features that suggest that it may be part of an inherited connective tissue disorder similar to the hypermobile form of the Ehlers-Danlos Syndrome, formerly called EDS III. It probably is EDS. At the present time we simply do not know for certain whether or not HMS is merely a less severe type of EDS III. Pain can occur in other forms.

It is often accompanied by an intense sense of exhaustion. the severity of the pain we  feel is greatly influenced by our state of mind. If we are upset or agitated it tends to  increase. If we are content, relaxed or just happy it tends to diminish. The HMS/EDS people are often in the former category, and for good reason! Lack of understanding of the condition is widespread, and this, coupled with failure to receive adequate treatment for relief of symptoms, leads to frustration, resentment, anger (and lots more emotions which I could list but readers know them all only too well!) and, ultimately depression. These emotional influences can amplify pain, but they do not cause it.(Prof R Grahame CBE, MD, FRCP, FACP. University College Hospital, LONDON)
http://www.ehlersdanlos.ca/hyperpain.htm

Joint hypermobility results from genetic variations in connective tissue matrix proteins resulting in stretchier tissues. For many it is an asset that confers greater facility for physical prowess. Others, less fortunate, fall prey to the associated effects of tissue fragility. The most frequently encountered constellation of traumatic and overuse injuries is termed the (benign joint) hypermobility syndrome (BJHS). This condition, poorly understood, frequently overlooked, misdiagnosed and inappropriately treated, is the  cause of much needless suffering and anguish. Accumulating evidence suggests that  JHS represents a forme fruste of an heritable disorder of connective alongside Marfan syndrome, Ehlers-Danlos syndrome and osteogenesis imperfecta, with which it shares many overlapping features, but from which it can be phenotypically distinguished on the basis of clinical features and prognosis. The responsible gene defects have yet to be elucidated.(Grahame R. "Hypermobility--not a circus act" Int J Clin Pract. 2000
Jun;54(5):314-5.