One of those things where I'm not sure what really caused it! Came home from work and started talking to a friend walking past, turned a little bit and it went. Knocked my breathing, couldn't walk! Tried to get down on all fours to stretch it out (thinking it was muscular) but soon as I was on the ground I was stuck!! My brother found it amusing as he had to wedgie me onto the chair! Physio starts on Thursday so no playing with the Z for a while sadly