If your engines oil pump is bad or is failing and not providing enough oil pressure for your engine then you should not continue to drive the car until you have the oil pump replaced.
The cars engine needs the proper amount of oil pressure to lubricate the engine properly and when the engine is unable to get enough oil pumped through the engine you risk seizing up the engine.
So if you do have a drop in oil pressure and are driving then try and get the car to a mechanic as soon as possible to have it checked out.
Sometimes a dirty oil filter could be the culprit of low oil pressure but if it is the oil pump then driving the car with a bad oil pump will damage the engine in a short time so avoid driving the car too far with the bad oil pump.
When your engine is losing oil pressure it needs to be checked out immediately to avoid damaging the engine which is more costly than replacing the oil pump.