Оригинал
There is a lot of debate on this topic. The consensus so far seems to be: hereditary, impact/injury, connective tissue disorders, and pressures in ones cerebral spinal fluid and way of body coping with shifts in it.
Personally, I don't have it in my family,and I have no connective tissue disorders. I do tend to fall often even in childhood, but somehow nothing seems to stand out in particular.