As far as well-bred field dogs, I've maybe had 30 or 40 out here total.
Only one with EIC. My own dog, now 8 years old. Textbook EIC. Nothing really mattered except his excitement level. Dropped a total of maybe 5 times between the ages of about 2 and 4 or 5. One time on purpose to do testing, biopsy, etc.
Would start to wobble, but be completely coherent. One of the classic signs, in my non-vet opinion, is that it's clear that their brain doesn't realize their body isn't working. An overheated dog tends to just quit, period. An EIC dog attempts to keep working. Once they drop, they're back up to full capacity, completely unaffected, normally within 10-20 minutes. Even though it's not heat-related, we would always ice our dog down because we worried we would misdiagnose an actual overheating episode.
I only have experience with my one dog, but it is so different than the few times I've seen dogs overheat.
The vet we were working with at the time felt that it was related to adrenaline, something on the cellular level.
I can say that our EIC dog is definitely high strung. When he was young, we couldn't let him sleep in bed because he would just lay there and pant (and we keep our house really cold). He wasn't high strung in a misbehaved way, he was just exciteable. Even today, when we go to the kennel, he's bouncing around, making noise and sometimes barking to be let out, even though he knows better. He's a master hunter and we never had any episodes at events, but Lisa Styles (who's on here occasionally) has a dog that seems to be more affected than Woodie. I know her dog, Loukas, even went down in water at least one time. That's really scary. Woodie never did that, thank God. His seemed to be only in the most exciting cases...
It's a very scary thing. It's very hard to watch. I wouldn't wish it on anyone.
-Kristie