Sorry to hear Paul but like most people I also pulled my back playing my one and only game of squash and I carried on as it just went numb, in bed for a week after but it got easier by the day. Remember even though painkillers make you feel better, you're NOT it just masks the pain of the injury so let it take it's course.
Good advice on icing and rest, sleep on the floor or a board to stop your back sagging. Hope you get well soon.
BTW was the spanner in your wallet???