I've had it 3-4 times, it's not fun. Of course, I'm not in my athletic prime (I don't think I had one).
My son was a high school wrestler and won a varsity spot as a sophomore at 171 pounds. Anyone who knows anything about high school wrestling knows that those guys, if nothing else, are in shape and generally recover from stuff pretty quickly. He caught pneumonia over Christmas and to make a long story short, he really wasn't back to normal until March, after the season was over.. Slower, less stamina, etc.