It's good news! Her heart is perfectly sound, there are no structural
abnormalities, no "hypertrophic myocarditis" aka enlarged heart, nothing
wrong at all except ...

After cutting back on the Tapazole (from 5 mgs twice a day to 5 mgs once a
day) her heart rate is back up to 300+. I had cut it back because her
appetite fell off and she threw up one dose, and most people I asked said 10
mgs a day was high.

The vet says the high heart rate alone could cause fainting episoded due to
arythmia and possible fibrillation. It makes perfect sense that she would
have had a fainting spell before being on Tapazole then one after the
Tapazole was reduced by half.

He prescribed a beta blocker and told me to go back to the 10 mgs of
Tapazole per day. I have a feeling just increasing the Tapazole will
probably reduce her heart rate, because it did at the higher dosage--it was
down to 230 at her last checkup.

He also told me not to even think about a brain tumor, because her behavior
is not abnormal--for a cat. When I told him about the "mow mow mow" head
wagging thing he immediately asked "does she bite her arm?" And I said
"Yes!" He said "it's called feline hyperesthesia. Perfectly normal."

Thanks to everyone in both groups for helping. The ultrasound (here in
Raleigh, NC) was $245, and worth every penny to put my mind at ease. Now we
can slowly reduce her weight and hopefully prevent future heart disease.