I'm so sorry to hear Trixie is ill. It sounds like things must be serious. What signs are you seeing?
Has she ever had any illness previously?
I see. Well, aneurysms are possible in dogs, but very uncommon. My first two thoughts would be either undiagnosed heart disease or a neurologic problem such as seizure disorder.
I'm very glad you were able to get her to the vet. I would certainly start with a physical exam, and would also like to do blood work immediately.
If these were normal, I would continue with imaging of the chest using x-ray.
Do you know if they've done any testing yet?
At this point, I would say her prognosis is guarded until we get a diagnosis.
When you say she is sedated, do you mean they gave her sedative medication?
IV fluids are a good idea as long as she doesn't have a heart condition. I'm surprised he gave her sedation, it sounds like she was already very lethargic/unresponsive when you had found her.
Was there any vomit or feces in her run?
I suppose another possibility would be anaphylaxis, she could have been bit or stung by an insect while in her run and had a severe reaction.
Perhaps a spider or stinging insect like a bee, wasp or hornet.
With the weather, a spider might be possible. The other flying types not as likely.
I don't know that I've ever seen a dog in that condition after a reaction, but I'm trying to brainstorm other possible causes for you.
I understand. I highly recommend requesting some blood work and also ask your vet what he thinks of her heart at this time.
You can certainly get back to me later if you have any test results to discuss.
Great. Good luck with your little girl. I'll be thinking about you.
I'm so sorry to hear that. I hope good memories of Trixie will help to comfort you at this time.