My dog thinks she's pregnant - I hope

My beloved dog is going through a stage of lethargy and moodiness. Since she is turning 10 soon, I sure hope it's nothing more than the after-stage of being in heat. Female dogs can think they're pregnant after they've been in heat, because their bodies have gone through their mating period during which they would have been "knocked up", so to speak, if one had wanted to breed them. Well even dogs who aren't bred and get pregnant can go through a stage when their bodies believe they are pregnant and they start to act accordingly. Kelly has gone through this before. The first time we were really worried because she gets very lethargic and her breathing seems laboured and she doesn't want to eat or even go for walks. We had all kinds of tests done on her but the vet couldn't find anything wrong and explained the process of fake pregnancy in female dogs to us.
What worries me is the usual thing that still bothers me even though we've gone through this numerous times. What if isn't fake pregnancy? What if she's sick? What if she's dying? She is getting up their in age.
I hate this so much. This is definitely the one huge draw back about having pets. They will get sick and when they are you feel so powerless, and eventually they will die on you. I've had birds die on me and that was terrible, I'll never forget it. It will be infinitely more difficult losing Kelly. I think I'll want to die as well.
I don't just love dogs, I fall in love with them. I love them with an intense passion that I often don't feel for people. There's nothing better in this world than animals, dogs especially. I act like a lunatic when I meet dogs in the street. I stare and turn around and keep gawking, so that the owners must think I'm crazy. Sometimes I laugh out loud and talk to myself. I talk babytalk to pictures of dogs and cats, as though the animals were right there in front of me, in the flesh.
Everything just seems so much better if there's a dog present. I can endure a lot more if there's a dog around. I can even tolerate people I would normally not care to be around if they have a dog that I particularly love. All I need is the presence of a dog and I feel happier and more peaceful. Once they are around me, I can't leave them alone. I'll ignore the owner and devote almost all my attention to their dog. I can be quite rude.
Having a dog is great, but is it worth the pain of them dying?