Just needed a soft reboot. No really, some obstruction interrupted the flow of fuel and your engine switched to sucking engine oil out of the crankcase through seemingly well worn piston rings.. There is a long list of possible causes from dirty fuel tank, clogged fuel filters, water in the fuel, sticking high pressure pump, etc. I would start by replacing the primary and secondary fuel filters. A runaway diesel can be catastrophic; blocking the air intake tube with a large rag will quickly shut the engine off. Try to locate the cause, because this will tend to happen again.