Was it just last night that she was acting like this?Any vomiting or diarrhea?Has she been urinating and defecating normally?Is she spayed?
Is her belly hard to the touch or soft?Does she have any underlying health issues?
Thanks for getting back to me -
She's had lesser versions of this over the past couple of months, although the open-mouth breathing seems much more pronounced last night.
No diarrhea, and no vomiting last night, although when this happened about a month ago, there was some vomiting.
Urinating and defecating normally.
She has lots of lumps, so that one is tough to answer.
She's just really old...she has chronic ear infections, and that's been acting up lately.
Does she have any other odd behaviors...staring at walls, or seeming confused?
Is she on any medications?
Thanks for answering my questions.
The symptoms you describe sound a bit like Canine Cognitive Dysfunction, which you can read about here: http://www.cdsindogs.com/CDSInDogs.aspx?drug=CC&country=US&species=OO&sec=000 , and since we often see it in older dogs, it's the first thing that comes to mind when I hear about a dog who is having unusual behaviors in the evening.
Additionally, some dogs get a little anxious at night for reasons we really don't understand. At our clinic we refer to it as 'sundowning', where the animal is fine all day, but then becomes restless and agitated at night.
If your girl hasn't had any blood work done recently (specifically a thyroid test) I would suggest that be done. Underlying medical issues such as organ disease or thyroid impairment can lead to a change in behavior in older dogs.
Something you could consider would be talking to your vet about a light sedative for your pup in the evenings. One that we use is called Clomicalm and really seems to work well. I like it better than the Aprozolam because it seems to have a more consistent way of working.
Another supplement you could try would be Melatonin. This is an over-the-counter drug that can be used to treat some anxiety issues in dogs. The dose you would give would be up to 3 mg given orally whenever necessary up to every 8 hours. More information can be found here: http://www.petplace.com/drug-library/melatonin-melatonex/page1.aspx , which includes risks, warning signs to watch out for and other bits of useful information.
If you'd rather not add another drug to her daily regimen, you could try something like the DAP collar. These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.
I've used the DAP collar in my own dogs and with some of the dogs I've rehabilitated and I really, really like the results. Just keep in mind that the collar only lasts for 30 days, so you'll have to replace it monthly if it works for you.
I hope this helps.