Happened to me last week. Food poisoning, 2 days of vomiting and lots of fruitless retching resulting in some sort of scratch or something on my lower esophagus (my diagnosis). Could not eat - or barely swallow Gatorade. Bad pain, to make you bend over, grimace, and utter bad words.
Luckily for her, Mrs. BD was in wonderful Milwaukee having a fun time with pals so did not have to participate, help, or be inconvenienced by my misery. Seems like a cool town. I got a Harley sweatshirt out of it.
Was able to handle some soup on Sunday, so got back to gym on Monday having lost 6 lbs. Still little appetite, but that's sort of normal for me because I love tasty food but only in small volume. It takes very little nourishment to keep me in good shape despite daily workouts.
My point is that a week+ illness can measurably set back your strength and fitness in a way that a 10-day gym-free active vacation can't. This week I have been worse with everything - weights, cardio, calis, endurance. It could take me 3 weeks to get back to where I was. Slowly.
Imagine the effect of a year without challenging exercise. Terrible, soft, lazy. Nobody wants that.
I bitched to my genius trainer that it's a damn shame that fitness doesn't just ratchet up - and stay there. He said "We're biological, not mechanical." Duh. I know our bodies are coded to self-destruct after age 35 or 40. I thought that if it all ratcheted up, we gym rats would all look like the Incredible Hulk. We'd be amazing specimens.