A family member had the misfortune of getting one twice (at a distance of many, many years), and it took quite a while to recover.
I got a really hard pneumonia few years ago. It took several days in hospital to find an antiobiotic which actually worked, and I was in pretty bad shape in ER when it finally started to work.
It took 10 weeks to recover back to work, and over a year before lungs were back to normal, confirmed by x-ray.
Pneumonia can be deadly, even for healthy young adult.
I personally still have a wheeze (slight, but it's there) from a cold I had years ago. If someone asked me to self-report it as part of a "long-haul rhinovirus" study I might, but nobody ever looks for that.