I've gotten pneumonia almost every winter from 1998 onward.
First time was uber bad... spiked a fever of 103.7 and it went up to 104/105 before they could get it down. My lungs were almost 90% full of fluid, so they stabbed a tube through my ribs to drain it out. It took about 3 months to fully recover, but I was back in training about 1 month later.
None of the other times have been anywhere near as bad. It typically starts off in my sinuses, moves to upper respiratory, and then sinks lower. I don't even bother to go to the doctor's unless I can feel that my lungs are at least 1/2 full of fluid. I also rarely get more than a lowgrade/midgrade fever. It's always fun to watch the xray tech's face when I go in all chipper, announce I've got pneumonia, and then have their faces change as they look at the xray. (I've got swimmers lungs... even at 1/2 full I "blow" more than most people do with clear lungs). Then I get a z pack (azithromycin), and am all better by a week later.
Honestly, I prefer the "worse" cases of pneumonia... because with a zpack I'm healed in a week or two (aka about a week to get sick, and then a week of meds)... but when it's low level pneumonia, it can drag on for months.
After having gotten it so much, I know my personal "triggers" (walking around with wet hair in the winter triggers it ALWAYS... my doc and I figure that the bacteria probably just 'hibernate' in my sinuses, and when my head cools down enough ... they kick into high gear). We've tried mega doses of a couple different kinds of antibiotics... in addition to the pneumonacoccl vaccine... but nothing has managed to wipe it out.
TYPICALLY... when being screened for pneumonia they have done 3 tests on me: the "blow" (blow into a tube that registers how much air I'm able to move - which doesn't "work" on me, because my lungs are so big, a blood test to test O2 levels in my blood -again doesn't work on me so much, because of my lung capacity-, and an xray. They'll also usually draw blood to test for other infections. But that takes 4-10 days of labwork, and the xray has always been definitive. LOL... if you've got fluid filling up your lungs that's readily apparent on the xray.