Yes, you can get the flu more than once but there are so many flu viruses and each of them can mutate to slightly different forms quickly that even though you won't get the same exact flu more than once, you could get a new variety or mutated form of the initial one.
Pneumonia is a general term, not a specific disease. There is viral pneumonia, bacterial pneumonia, and a fungal pneumonia, among others.
walking pneumonia
There is no opposite of pneumonia.
Bilateral pneumonia.
This type of pneumonia is also called atypical pneumonia, walking pneumonia, or community-acquired pneumonia
You should say, "I recovered from pneumonia."
Multifocal pneumonia means that there are patches of pneumonia throughout your lungs as opposed to lobar pneumonia which is contained in one spot.
I once had pneumonia.
pneumonoultramicroscopicsilicovolcanoconiosis (pneumonia)
Pneumocystic carinii pneumonia
Pneumonia is a disease of the lungs. Fish have gills and do not have lungs. Ergo! Fish can not suffer from pneumonia, so pneumonia can not kill fish.
Pneumonia is a respiratory disease, rather than a place or state, but there are a few entries on Google maps such as "Pneumonia Lake", "Pneumonia Gulch" and "Pneumonia Road" that are named after the disease.