You have described to me a Catahoula/Australian Border Collie mix that is 2 yrs. old and has had 2 seizures in the last 3 months. As long as she does not have another seizure tonight, you don't need to take her to an emergency vet tonight, though she should see her family veterinarian in the next few days.
Let me explain....
Seizures can be caused by a large number of different things. Some of these things are things INSIDE the brain, and some are by things OUTSIDE the brain. Examples of things inside the brain are infections and trauma (a recent hit on the head), and epilepsy. Examples of things outside the brain are low blood sugar and certain toxins.
The way we determine what is causing the seizures is to start with checking to see if this is caused by something outside the brain. This is done by taking a blood sample and running a number of tests. The vet would check yourdog's liver and kidney function, check for diabetes and test her for various parasites (which can migrate through the brain and cause problems).
If these were all normal, your vet might suggest further testing aimed at seeing what is going on inside the brain. These tests might include a CSF tap to get a sample of the fluid around the brain, and/or an MRI of the brain. Many owners find these brain tests prohibitively expensive, and may elect to attempt treatment without test results. In that case, the vet would make a tentative diagnosis and start treatment (such as phenobarbital if epilepsy were suspected or prednisone if an inflammatory condition were suspected).
With a sudden onset of seizures in a dog of this age, my top two considerations would be EPILEPSY or an INFLAMMATORY condition (GME - more below). However, the seizures could be evidence of an an electrolyte imbalance (such as low potassium, which can happen with kidney problems).
After the dog has recovered from a seizure (usually this "post-ictal phase" lasts less than an hour), she is back to her normal self.
I'll give you links to more information about seizures:
And about epilepsy:
and about GME:
Often, when seizures start, they are many months apart, and start getting closer together very slowly. We generally treat an animal once the seizures are closer than one a month. We usually recommend that a dog come in for testing after she has had two or more seizures. The goal of treatment is to keep the seizures at no more than one a month, so treatment might not be needed at this time with your dog if this is due to epilepsy, which would be at the top of the list of possible causes.
Here are some ideas on how to keep her as safe as possible during a seizure:
The other thing that I should mention is that it would be very helpful to your vet if you were able to video tape an episode! It really helps to be able to see the whole patient during an episode, but also to see her face and jaws and eyes during the episode.
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.