Surfer's myelopathy

Surfer's myelopathy is a rare nontraumatic paraparesis. It is a spinal cord injury caused by hyperextension of the back. When the back is hyperextended, a blood vessel leading to the spine can become kinked, depriving the spinal cord of oxygen

The condition gets its name because the phenomenon is most often seen in those surfing for the first time, but it can be caused by any activity in which the back is hyperextended (yoga, pilates, etc). In some cases the paralysis is permanent. As of 2007 there were 9 recorded cases but the number of people actually afflicted is higher. A study of 23 cases was published in 2013.