If you haven’t had it you won’t understand. I can’t swim but if you’re a swimmer you might understand a parallel - it’s like not being able to swim - your head bobbing on water surface, sometimes you can breathe other times you are just gasping. If you’re in water the people will see you’re drowning and a life guard will pull you out.
Pneumonia is this “almost drowning” for weeks!and then bring barely able to breathe for months.
Again: fear is exactly the right response to pneumonia!