Oil meter drops when stopped

I have a 97 Dodge ram and when i stop , my oil meter drops to 0, then when i accelerate it goes back, then as i slow and stop it drops again, giving me an oil light, why?

First guess would be "how old is your oil"?
2nd-How many miles?

Update is im an idiot, i added a quart of oil and jts back to normal , thanks guys. Has 227k miles