I see health as being in a normal state of sensation. Being aware of your homeostatic level and knowing when it has deviated or knowing where your daily set point is at. An illness is the presence of a factor that causes you to feel uneasy, non homeostatic, or simply not normal. For instance when you wake up every morning (usually) you feel a bit tired and groggy but other than that feel nice and healthy. One day if you wake up in the morning with your nose congested or you’re sneezing you know that you have an illness because a regular “normal” feeling has changed and you feel a different stressful sensation. This leads to you having to take some sort of supplement whether it be tea, cough syrup, or aspirin to return to a set point.
I based this reasoning on my own personal experiences, when I was a child (I’m not sure why) I would constantly get ear infections. It got to the point where the day before if I already had the flu and felt my ears had this tingly sensation I knew that I was going to have an ear infection. Surely enough I would wake up the next morning to the throbbing,popping, and agonizing pain (or so it felt) of an ear infection. I would go to my doctor and get some antibiotics and pain reliever that helped with the infection. Using that as a criteria I defined an illness as that early morning feeling of “oh man I feel terrible” and having to use something to feel normal.
I chose infertility as something that is hard to categorize as an illness because many people who are infertile are asymptomatic they show no signs of being “ill”. They go on most of their lives without knowing that something is wrong. But then its becomes a problem when said people try to procreate and cannot succeed, so indeed something is wrong but their daily sensation of health is unaffected.
Another one would be old age, to me it seems like a normal phenomenon and that every life form experiences some sort of senescence. Although the individual may feel fatigue and other pains. It’s something that must become normal for everyone or that eventually becomes normal for us as we age.