Let me start by saying that ALL dogs deserve love whether they are healthy or sickly. In my opinion, the sickly ones even deserve more attention. But all the signs mentioned in the video are also valuable so as to tell if your own puppy is unwell.
1. The puppy should have no discharge from its nose and eyes that are bright and clear. There should be no gunk in the eyes or any tear stains.
2. The puppy’s ears should be clean inside, with no sign of redness, irritation or discharge. A bad smell from its ears, or constant scratching at them or head-shaking are a red flag for ear mites or infection.
3. Its coat should be clean, and shiny with no bare spots or red irritated areas because these indicate skin problems or allergies.
Also, keep an eye on the behavior of the puppy, it should be frisky and energetic. A pup who just seems a little shy than its litter-mates is probably perfectly healthy, but one who is disinterested in you and the surroundings could be sick. Normal puppies are friendly, curious, trusting. They mill around your feet, tug at your shoelaces, crawl into your lap and nibble on your fingers.
In the end, use your best judgement when trying to help your puppy get back to normal, and never hesitate to let a vet take a look. Better safe than sorry.