Exactly!
Trust me on this, You did exactly what your dog wanted you to do.
The way I see it, there can be no conclusive studies on this subject. I cannot offer proof of a “future-oriented mental state” (unless you want to say that squirrels hoarding nuts in order to get through the winter is a future-oriented action) of my dog, but there definitely is a self-concept: When he was having a fever, he did not recognize his mirror image anymore and started to bark at the “other dog” he saw in the mirror. It can be concluded that in a healthy state, when he can see his mirror image but doesn’t bark at it, he has a sense of self, allowing him to know that this is his own image in the mirror.
I think what you’re attributing to self-awareness is from other factors. Perhaps when he’s sick, he’s a little more jumpy about another animal around because he is less able to defend himself, and so he barks to scare it away. When he was in good health, perhaps he recognised that the animal in the mirror is non-threatening, and decided not to bark. Any number of things could have attributed to your “evidence” of self-awareness.
Jess
My personal and professional opinion is that euthanasia is the last gift of love and respect we can give our pets. It releases them from the agony and indignity of a slow, painful death. Sure it’s unnatural. Domestication is unnatural. Dog chow is unnatural. Vaccines and antibiotics and doggy seatbelts are unnatural. The entire life of the modern dog is unnatural, in point of fact. There’s no reason to go all natural at the end. Besides, who ever said natural was necessarily good? I mean, smallpox is natural, but I sure as hell don’t want it. Hemlock is natural, but somehow I doubt you’d drink a big glass of it.
What it all boils down to is this: when we take a pet into our hearts, homes, and lives, we take on the responsibility of giving that animal the best quality of life we can reasonably provide. That means we provide food, shelter, veterinary care, attention and affection. It means that we do whatever we can to prevent that animal from suffering. We provide pain medications during illnesses and injuries. We provide preventive care to avoid painful medical conditions. And when the animal is in horrible pain and there is no hope (or we can’t afford the treatment) we euthanize instead of leaving it to suffer. To do any less is not only a dereliction of our duty, it’s cruel and inhumane. To put it bluntly, keeping a suffering animal alive because we don’t want to let go is really fucking selfish.
Assuming that a dog is a higher animal, look at it from this point of view: when you’re blind, deaf, fecally incontinent, and so arthritic you can sometimes can’t manage to get up out your own filth when you soil yourself, do you want to go on living like that? When you’ve got metastatic cancer and are in horrible pain, do you want your doctor to give you some pain meds? Remember, oxycontin ain’t natural. When you’re looking at the choice between a lingering death, spending your last hours shrieking in agony and shitting and pissing yourself uncontrollably, would you really choose that over a painless injection?
It is merely one example, the one example that just sprang to mind. Still, I conceded that there can be no conclusive evidence, meaning to say that people who want to believe that animals are some form of unintelligent bio-robots will always hide behind that last shred of doubt that it simply cannot be proven to everyone’s satisfaction. That said, there is no conclusive proof that everyone else but me has got self awareness: I cannot look inside of your thoughts, so how do I know that they are there? I guess when push comes to shove this topic will be - like religion and whether George W. Bush is a nice fellow - strongly depending on one’s own opinion. I made my position clear and others have made their position clear 
Back in January, I had to make the same decision. One of my beloved 15-year-old cats was suddenly lying on the floor, partially paralyzed, incontinent and wailing horribly. I rushed him to the nearest animal hospital, where they examined him immediately. The doctor explained to me that the cat had a blood clot in his aorta, and was experiencing something like a charleyhorse, but all over. She could keep him alive, but his quality of life would probably never return, and even if it did, he would suffer a lot in the mean time.
I immediately told her that we had to put him out of his misery.
Afterwards, my mother commented that it must have been a really difficult decision for me.
I told her no, it was the easiest decision I ever had to make. As sad as it was (and I still cry over the loss), I had absolutely no doubt that I was doing the right thing.
That’s one way to look at it, Rex, and I suppose one could say that in the same way, our cat Frisco was killed also.
But at the time, Frisco was on oxygen, nitroglycerin, and Lasix (congestive heart failure and fluid in the lungs), and no matter how we looked at it, he would never again run or jump or play or chase his toy mouse or sleep in the pool of sunshine coming through the window. If he continued to live, his life (and bless him, he was only ours for four years), would never be the same as it had been.
The way we saw it, we had two choices: either to euthanize Frisco, or let him hang on however he, and veterinary science, could. The latter almost certainly meant pain; the former offered release. We opted for euthanization, and Frisco slipped off into eternity snuggled in my wife’s arms. It was the least we could do for our little guy.
Against nature? Perhaps, but I suppose that Frisco’s life was against a cat’s nature. He was an indoor cat–he had been “fixed,” he never hunted and killed and ate anything, he scarfed down his store-bought cat food and drank his tap water. He played with manufactured toys and scratched his claws on a cardboard scratcher. He watched the seasons pass through a window, and seemed to be content to leave them outside.
After such an artificial (for his species) existence, we’re supposed to insist on nature taking its own course to his death? No, I don’t think so.
It’s trite to say so, I guess, but it really is an act of kindness. We accept the responsibility for our pets, and we must also understand that that responsibility also means that if our friend is going to suffer, we owe it to them to let them go gracefully, and with dignity.