Healthy Cats Acting Sick

In the latest issue of DVM Newsmagazine there was the oddest article about a study done at The Ohio State University, in which they discovered that healthy cats who were acting sick improved with environmental enrichment.
OK, wait a minute. Healthy cats acting sick? If the cats were acting sick, how were they healthy? The article doesn't say. So let's suppose that the cats were normal on physical exam and had normal blood and urine analysis results. Because if they were truly sick, something would be abnormal there, right?
Wouldn't it be nice if that were true?
The public may not be aware that a common presentation for a veterinary patient (that's medicalese for why you took your pet to the vet) is ADR - ain't doing right. Often these animals are "normal" on physical exam, and have normal laboratory results, and get sent home without treatment because there appears to be nothing to treat.
Is that the same as being healthy? Having no detectable signs of illness?
Go to a doctor's office. Let's suppose that someone is there because there is something wrong with them. You can look at this person, you can touch them, but you cannot ask them any questions, such as "How do you feel? What is bothering you?" If all the laboratory results are normal, and the person looks okay, you tell them they appear to be healthy and can go home now.
Do they have a headache? How would you know?
Are they depressed? How would you know?
It seems to me that we should give these nonhuman beings a little more credit, and assume that perhaps there IS something wrong with them, even if our crude diagnostic tests and rudimentary physical exam indicate otherwise.