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Hopefully you were able to read the answer I gave but if not let me know. Seizures are rarely fatal unless they occur for long periods (generally over 5 minutes) or occur one right after the other because that can cause overheating of the body and brain damage. Unfortunately there is no way to know when a seizure will occur, there are no signs before they happen so there is no way to prevent one without medications.
Seizures cause so much twitching and heating in the body that many dogs will pant afterward. It's basically like running a marathon and takes a lot out of them. Typically the panting will resolve fairly quickly as they relax. However, if the panting persists for more than 30 minutes after a seizure then it could mean another internal problem causing the seizures (such as an infection or liver problem) or that the body is overheated from the seizures. Some dogs can get a temperature over 108 degrees after a violent or prolonged seizures (the normal temperature for a dog is 101 to 102.5). The bloodwork the vet is doing is look for problems such as the infection or liver issues.