Two things I suppose - how can riding hurt your back, and how do you ride with a bad back?
I'm not sure how it happened, had fairly uneventful hack - stirrups were a bit too long but too lazy to change them once on the way - no shying or abrupt changes of direction, which often yanks my back painfully. He was a bit strong and had to pull back like mad but nothing unusual.
Apart from dismounting at block, what can I do to minimise further pain? Is an old old problem that hasn't troubled me for over ten years, don't fancy making it worse. Mainly very lower back, hips, pelvis.