FWIW, I drove a '94 E420 to 300,000 miles and had to replace the oil pressure sending unit 3 times. The first time it did it, it scared the... well, I was SHOOK!
I was driving down the interstate and noticed that the gauge wasn't pegged. Ten miles later it was almost on zero after jumping around erratically. A local independant mechanic actually made a fitting adapter with a tap and die set so that he could hook up a manual guage and confirm good oil pressure. I drove the 100 miles home and had the sender replaced the next day.
A varient of this scene happened twice more (without the panic) while I owned the car. Iwould suggest, however, that you address this ASAP. If it is not the sending unit, continuing to drive the car can only add to the problem.