I get my flu shot every year. Last time I had the flu was about 6 years. Never got officially diagnosed with the flu, but I'm pretty sure it was legit (vomits, shits, aches, congestion, and was about a week of hell, and another 2 weeks of not quite hell but still sick).
Just last weekend I got some kind of stomach virus. Vomiting and diarrhea. Aches so bad it felt like my entire skeleton was on fire. It was one of, if not the, most painful and uncomfortable nights of my life. Nights 2 and 3 weren't nearly as bad, and I was back to 100% by day 4.