Every time I look at Leah lately, I want to cry.

As Leah approaches twelve, I notice she isn't herself anymore. Her symptoms are rather vague, and I guess the best way to describe her problem is that she has just been off.
She's always been aloof with visitors and strangers, she's never been thrilled about being crated, and she's always had a high prey drive. Recently, however, those quirks seem to be escalating. Leah will no longer tolerate the cats running in the house, chasing after them if they move too quickly or surprise her while she's sleeping. At NoseWork class, although she initially disliked being crated and let everyone know it whenever they walked past, she now freaks out if someone just stands too close to her crate or merely makes eye contact with her while she's inside.
Her response is to bark threateningly at the offender, often causing the unsuspecting person to jump out of their skin.
I've tried covering the crate, to no avail - she just erupts when she hears people or dogs walking by. The problem isn't only occurring at NoseWork either - lately, Leah has even been telling off guests at our home, giving them an earful if they stand in one place for too long, like when they are getting ready to leave.
Through careful supervision and management, I can prevent her from harming the cats or guests, (Leah has an awesome Leave-it - she's even dropped a live squirrel on Nick's command!), but it is the crate behavior that is troubling me most. Because that is something I can change. Currently, I'm considering dropping Leah from her NoseWork class. Although she appears to genuinely love the game and getting out of the house for some one on one 'Mommy and Me' time, I don't want her acting up or feeling stressed while in the crate waiting for her turn.
If she is having fun sometimes, but is stressed at other times, what is the right thing to do?
I joke with Nick that maybe the NoseWork is giving her too much confidence...possibly causing her pushy behavior, but I know in my heart that's not it. There's something brewing, of that I am sure. I mentioned her lack of tolerance to our vet, just a few weeks ago, at her annual exam. He performed her exam, and ran a thyroid recheck, and all came back normal. But Leah is also developing physical issues as she ages, and I wonder if they might be the cause of her behavioral changes.
Oh, how I sometimes wish dogs could talk.
Lately, Leah's been shaking her head intermittently, maybe once every two or three days. She's not scratching her ears, there's no odd smell wafting from them, no dirt when I clean them. I mentioned it to my vet, and he decided to treat her for an ear infection anyway, in case she has one that is just developing. She's been taking Mometamax for five days now, with no change. It's nothing major. A shake here, a flick of an ear there - if I wasn't watching for it, I probably wouldn't even notice it. But the ear medicine sure doesn't seem to be making any difference, so of course, given her behavioral changes, my mind drifts to something more insidious than a simple ear infection...
But I always jump to the worst case scenario, don't I?
Even so, I also think, would I want to know if something's there? I mean, what can be done, especially considering her age? And her age is starting to show...
Yesterday in the yard while I was working with Leah, jealous Toby decided to saunter over and attempt to hump her. This rude behavior of his normally results in either me grabbing him by the collar and telling him off, or Leah biting him and chasing him away - depending on which of us reacts faster. But this time, Toby had barely begun his advances, when Leah grunted and just collapsed. I chased Toby off and turned to help her, but she was already getting back to her feet. But she didn't chase him and punish him for his misdeed - which is completely unlike her. I examined every inch of her, pressing everywhere, her stomach, legs, spine, sides, neck...she didn't make a sound, or even turn an ear sideways. When I released her, she took off across the yard to hunt for feral cats - appearing perfectly normal in all regards.
But this isn't the first time Leah's fallen...
Over the past year I've seen her rear legs give out on her, splaying out sideways along the kitchen tiles in a horrific split. It hasn't happened often, maybe three times in the past year, but that's three times too many. And yesterday in the yard, it appeared more to me like she collapsed, rather than slipped, but it all happened so fast, who can be sure?
Either way, she's a large, long legged dog, and I worry that there might come a time when she can no longer walk.
Recently, I have also taken note that Leah groans a lot when she is first lying down trying to get comfortable. It's one of those things that dogs, (and people), often do as they age. She's been doing it for a while now, but for some reason it has been drawing my attention a lot lately, and I'm trying to figure out why. Is it happening more often? Is it louder? Several times during this week, I woke up to her grumbling as she shifted around in her bed in the middle of the night.
I can't remember ever awakening to her complaining before...
Also, earlier this week, and again last night, she made an odd noise while lying in her bed, similar to a cough, but not quite a cough. It more sounded as if she had hung her head over the side of her molded plastic doggie bed and throttled herself. I've been home most of this week, and I've kept a sharp ear on her since she's always at my side, and Leah is definitely not coughing or acting sick.
Whatever the odd noise was, it only occurred at night, when she shifted around in bed.
My first extinct is always to rush to the vet, and I considered taking her in this morning, but Nick remains my voice of reason. As he pointed out, Leah is getting older, and things are probably starting to ache. She just had a physical with her vet, and Nick and I have both examined every inch of her, pressing on her body, watching for any reaction, receiving none. She's eating well, eliminating normally, playing and patrolling as always. For all accounts, she appears happy and healthy.
So for now we will wait, and see...
Besides, there's really no one symptom that I can point out to my vet and say, this is what's wrong. Vague groaning. A slip here and there. A cough which is not a cough. A shake of the head. A bit less tolerant than usual. Yet I feel another vet visit is looming, and this time, I don't want to hear what they have to say.
Whether Leah has a health condition, or it is just her advancing age, neither diagnosis is good.
Old age - one of the biggest downfalls of sharing your heart with a dog. Every misstep is cause for alarm, every symptom a warning. Worry becomes your constant companion. I'm trying to enjoy every moment with her, cherish the time we have left, but every time I look at her, I ache with the knowledge of the loss that is yet to come.

Why are their lives so abrupt?
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