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I agree with your vet that this could be a symptoms of focal seizures. And even though she's not striking at flies, she could be having the same symptoms and need the same treatment.
Phenobarb is not necessarily a bad thing, even in young dogs. Once the meds level off, most dogs have no problem with it being depressive or changing their energy level.
I would see the opthamologist for a good ocular exam to rule out detatched/detatching retinas and then go from there with the meds.
Let me know if you still have questions or concerns that I can address.