It could be in the gauge, but the gauge going down when you give it the gas is not a good sign. Either low on oil, pump sucking air or a bearing spinning. I would check the oil and make sure you are getting an accurate reading. False readings often come from oil splashed up in the dipstick tube. If you are sure you have enough oil, put a master gauge on the galley where the pressure tube screws in. Verify the pressure. If it is indeed fluctuating like your gauge in the dash, drop the pan immediately and see what's going on before before something bad happens.
