Dog Training Tips: Knowing how to tell when your dog is sick
One of the most important skills in dog ownership is being able to read your dog. Do they have to go out? Are they in the mood to play? Are they sick? The last one, in particular, is usually the hardest, as it's a choice between a possibly expensive trip to the vet just to find out nothing's wrong, or having a pup get worse because you hoped for the best. Sadly, as it's a financial choice, it's never an easy one.
In most cases, though, it's worth the financial burden just to be sure, especially if your dog has been sending some strong signals. Shivering (more than usual, in the case of smaller dogs which shiver anyway), changes in personality, lethargy, these are all signs that something is wrong. Sometimes this can be a cold, but if it's been going on for a long time it's time to see a vet. Some people are tech savvy and think checking on the internet is good enough, but this can lead to more harm than good, especially if you're seeking comfort and will be biased towards "everything will be okay."
This is to say nothing of when your dog gets into the trash/pantry/medicine cabinet/random trash on a walk. There are many things which are a-ok for humans but are potentially deadly for dogs, including but not limited to: garlic, onions, grapes, caffeine, painkillers in general, cooked bones, some nuts, etc. If your dog has eaten something he/she wasn't supposed to and you're not sure if it's potentially lethal, the internet turns into your friend (as opposed to above). If you see anything, anything, pointing to it being an issue, it's best to heed that warning. In a lot of cases, it's as simple as inducing vomiting.
tl:dr dog health is important, and knowing how to read your dog is the first step. Get to know what's normal, spot what's not, and your dog will do the same for you.
Prompted by this post on reddit's AskVet