Yes I unfortunately have experience with this.
About 6 years ago our lab mix had a seizure after we returned from walking, I called the vet, took her in and her diagnosis was Insulinoma, basically a cancer of the pancreas affecting how insulin is made. When her blood sugar got too low she would seize.
we took her to Angell Memorial in Boston as well as Tufts for second opinion, diagnosis was correct and ultrasound showed it has spread, so chemo was an option but not a cure,
to make a long story short, they gave her 9 months TOPS to live, I had her for another two years. I had to feed her frequently to prevent low bs, plus she was on some meds
then about 3 years ago, I took one of our other dogs ( again lab mix) to groomer/boarding place we use, she said Ginger had a seizure while there, So I took her in to be evaluated, hers turned out to have no specific cause, they became more frequent so she was put on meds.........anyway, she ultimately had a seizure during the night, that turned into clusters,and she died from that , about a year ago.
Its a scary thing to see them while in a seizure...........you feel so helpless.
Hopefully your doggies can be controlled with meds