I'm going to make the assumption that you did not pull the vehicle over to the side of the road when the pressure dropped below .5........correct?

And, you probably drove it at 60 mph for several miles with the gauge on "0".

If this is the situation, and the engine is still running, then you have successfully diagnosed your problem. Change the oil pressure sending unit and the problem will be cured.

If, however, none of the above occurred, then more analysis is needed to determine why you have low pressure on the guage.