Really sorry to hear this happened, but definitely have been through the same. I had a 6 year old GSP I hunted over with no problems what so ever, and was out on a quail hunt in eastern TX and exact same thing happened - he didn’t look right, slow to react even to my call and then he just collapsed and went into seizure. Same type scenario you described, just awful to experience cause you simply can’t do anything but watch and wait. Took him straight to an emergency vet, no big issues with tests run - Vet diagnosed as hypoglycemia since he had no previous seizures, was 6 years old and in overall stellar health. At time of that seizure, Sawyer was as I mentioned 6 years old, about 80-85 pounds with not an ounce of fat on his body. While the vet informed at the time (mid-90’s) that Sawyer could still be out in the field, I should be cautious and ensure proper hydration well before a days hunt (Gatorade actually was a suggestion). I hunted over him one more season, he had another seizure - not as bad as the previous year - and that was enough for me. Never had seizures at home and only the 2 I have mentioned - he lived 4 more relatively healthy years till I had to put him down. I wish you all the best with your dog and hope this helps in some way.
