Oil pressure is nothing to mess with, it's like blood pressure. To much not good, too little, really bad! However, the oil systems are alot more stable than the sending units used to monitor them, and in your case I'd:
1. Shut the motor off now!
2. Replace the sending unit (like $30 and a half hour labor and a six-pack) and start the motor and see if the symptoms go away.
Oh, obviously look around for massive oil leaks, but it sounds to me like your sending unit has gone stoopid.