2000 Ford Mustang oil pressure sensor

I have a 2000 Ford mustang it has close to 149 thousand miles. My concern is which happens is every time I get into the car and start it up my oil pressure idle or sensor stays down sometimes so for about 5mins of turning the car and off so I don't blow my engine away it goes back to normal then its fine for the rest of the day until I shut off my car and not use it for a couple of hours then I have to start the process again and sometimes it will be fine and I don't have to do it so can you tell me what this means and what I can do to fix the issue