I am having shooting pain in my back suddenly - it is on the left side, sort of middle (like back ribs). It kind of pulses, it doesn't seem to hurt specifically on the inhale or the exhale but a little of both. Am I dying?! Diagram of where it hurts:

ETA - I wasn't doing anything when it started. I was literally sitting still, facing forward, working on my computer. No sneezing, not one movement.