Can phnemonia run it's course and go away without treatment ?

Sure, or you may die: Depending on the severity of the lung infection (pneumonia) and your own basic health (ability to fight off infections), you can get better on your own, or you could die, or anything in-between, including a prolonged illness that lowers your resistance to other diseases/infections. If you're sick, you shoud see your doctor rather than trying to "power through." what if you fail?

Not really: Check with your doc. Natural history of disease may even cause death. Some patients recover without rx. But why play the odds? You need a doc.