First let me say that I am a veterinarian.
Doesn’t sound like EIC and have never heard of it in Weimaraners
Exercise-induced collapse is a genetic neuromuscular disorder characterized by muscle weakness, lack of coordination, and life-threatening collapse after intense exercise in otherwise apparently healthy dogs.
vgl.ucdavis.edu
It does sound a lot like epilepsy. Epileptic seizures are very common in dogs and generally starts between 6 months and 3 years of age. That is probably the best thing it could be. If they continue or get more frequent, usually meds can stop them. I generally don’t put on meds if they have them infrequently. Cause meds are 1-2 times daily for the rest of their life. If they have 3-4 a year, I don’t see a problem with letting them have them. Very rare for an epileptic seizure to cause death. The hacking can just be one of the quirks of your dogs seizures.
Can’t rule out DCM but I think there would be other symptoms. If he has That kind of heart failure, he would generally hack/cough at times otherwise than just when he was having an episode.
I have never liked grain free diets even before they were shown to sometimes cause DCM. Unless a dog is allergic to a specific grain, WHICH IS RARE, they prob shouldn’t be on a grain free diet.
The only good test for DCM is an echocardiogram (ultrasound of the heart). Easy and noninvasive but unfortunately expensive. Ballpark $400-500. Xrays and ECGs can narrow it down but echo l is the best test.
Best to visit with your vet about these concerns and come up with a plan to diagnose his condition. Unfortunately there is no “test” for epilepsy. But very few things incapacitate a dog and theN 15 min later he is up as if nothing happened. So I think most likely he has epilepsy. But my diagnosis without seeing him is worth what you paid for it