Oil Warning Light Possessed

I had an oil change by my usual mechanic. I drove away w/all fine. After about 10 miles, my oil warning light came on when stopped. I checked the oil, and it was full and clean. The next day, the oil warning light did NOT light. On the next day the oil warning light went on after about 5 miles, but only when stopped. My mechanic changed out the oil light switch, but it still behaves the same: no light for about 5 miles, then on when stopped. My mechanic wants to drop the pan to check the pump. The car runs and sounds fine-no pings or other unusual noises.

Any ideas?

Make, model, year, engine, and miles please.

I think I would want a mechanical gauge on that thing and now.  Don't assume it is the gauge, the actual  pressure could be be going low.  Maybe a pressure release valve?

Try putting a few more ounces of oil in.

Yes, get the oil pressure checked with an independent gauge, but I suspect a defective filter.

Your mechanic, or another mechanic, should check the actual oil pressure before doing anything else. Has this been done?

At this point you don’t know whether the oil pressure is low, or not.

Make, year, model, and mileage might help. You’re not giving us very much information. All vehicles are not the same.