koz is right, i think you burned all the oil away, or some sort of no-oil sensor detected and shut it off preventing internal damage, just keep an eye on the oil
i had the same problem with my old shadow, running and then just turning off for random amounts of time if i drove the crap out of it i would o through oil, as for it turning off , mine did the same thing , it has something to do with the bottom of the distributor there is a plug there (two wire black plug) on the bottom , not quite sure what it does but i had a mechanic fix it and ther car ran great after that.