Pneumonia can have many etiologies. Generally not, however there are exceptions. If you follow your physician's instructions explicitly, get plenty of rest, and take all the medications prescribed (even if you begin to feel better), you will most likely recover full lung capacity. If you continue to have a yellowish orbn greenish sputem after three days do not hesitate to bring this to the attention to your physician. Ocasionally bacterial pneumonia requires a short period of hospitalization and intravenous antibiotics. Drink plenty of liquids, walk around a bit, and take 1000mg of vitamin C every day. Don't worry too much.
If, during the night the difficulty in breathing gets worse, don't hesitate to call 911.
I am just guessing, but it seems like if you were diagnosed early and take your antibiotics or whatever the doctor has said to do, you won't have long-term negative results from a bout of pneumonia. I've had a lot of friends who have had it at one time or another, and the only risk is if they don't get treated.