Unfortunately, after several tests and 3 consultations with vet and vet-neuro, it's almost certain our Beasley has a brain tumor. There is a very small chance it's
late-onset epilepsy and an even smaller chance of a fungal infection,
but the tumor is the likelihood, due to his age. We aren't putting him
through costly neurological tests to confirm because, whatever they
show, the treatment for epilepsy and tumor is the same. The goal is to eliminate small seizures and keep the grand mal ones down to one a month. I guess the drug can really change personality and make them groggy, but we'll wait til it gets a little worse and see how he does in small doses.
As long as his adrenalin is up he seems fine, still enjoying runs, walking and eating, though he's become rather clingy. He also is sleeping well. It's when he's awake but trying to just stand or sit around that he jerks and trembles and has a hard time keeping his balance, or his legs will suddenly go out from under him. Hard to watch.
At least without the absolute confirmation we can hold on to the tiny hope that it's a mysterious case of late-onset epilepsy.
Thanks, all for your concern.
Do any of you have an experience of how long my dog might have left with a brain tumor, with good care?

Wow, Spencer's behaviors sound exactly like Beasleys. I will print your suggestions and bring to our vet, Dr. Crowe, tomorrow. Many thanks.

I feel better already. Thanks all. Though still unsteady as he's been the past few weeks, he's enjoying a sunny SoCal morning with all his usual rituals. I will post when I get vet results. Beasley would love the Haagen Daaz cure.

Our precious boy, Beasley, had a long (3 minute), severe seizure today, the first one ever. He is 13.5 yrs. He has since been very nervous and anxious. He's been rubbing the top of his head on the carpet for some time, recently has increased thirst, has been toppling over occasionally the past few days, and very stiff on the stairs, plus reduced appetite and occasional vomiting. The vet recently recommended teeth cleaning, which was done. From what I am now reading, he might well have a brain tumor, but he can still run 4 miles three times a week with great joy! He will be at the vet Monday when they open, but I dread possibly learning the worst. He is the dog-love of my life and I want him to live many more years.