I did try knocking the gauge and in this case, it didn't work. I took it into my mechanic to run an oil pressure check and look over the system. It ends up that the oil pressure sending unit was bad. It's a relatively inexpensive repair (about $300 - $350), which for my car IS inexpensive. Usually when I have to have something done, I'm dropping a thousand a visit and I really wasn't looking forward to that!!

 Thank you for the answer. It gave me something else to check before I resorted to the repair shop!