Sorry to hear that old chap. Deffo need a consultation with someone just to make sure you haven't snapped your spine in two.
Most likely a disc out (fluid joints between vertebrae) and fairly common. The good news is that it's easily treatable with some manipulation, rest and repair time. I knew a guy once put his back out hitting the bottom of the ketchup bottle.
Told you that you work too hard though. Anyway how big was the spanner?
Hugs.
C.