Hi Jack, is this a new problem that occurred after the oil was changed? And how many miles are on the vehicle?
To clarify, did this occur after the oil and filter was changed? This is important as they may have put the wrong filter on or the incorrect oil.
Jack, sorry I did not refresh my screen and sent my question too early.
On an engine with this mileage, a sudden drop in oil pressure while warm would indicate a worn mechanical component(s), such as bearings or the oil pump. I suggest two things-confirm the oil pressure drop with a pressure gauge hooked up to the engine. This will confirm you findings and rule out a faulty dash gauge and sending unit. Next, I would run a heavier weight oil, such as a 10w-40 or even a 20w-50. You may also use an additive with your current oil that may help, such at STP.
Jack, sorry I offended you by being polite. You have to expect that we will ask clarifiying questions in order to help you with your problem. If you knew the engine was worn, what else were you expecting??