Hi everyone..I'm a longtime beagle guy but I have a problem i've never encountered

I've had beagles for 25 years with many amazing days hunting and running my dogs. Right now I only have one dog, a 5 year old male. He is the only beagle we've ever made a pet. He lives indoors at night, something I've never allowed, but my 8 yr old daughter loves him. He is a great dog and a pretty good rabbit hunter. But he has had 3 severe seizures. None of my other dogs have ever had this problem. it doesn't seem to effect him when he is awake and he hasn't had one in months however he ocasionally shakes his head violently as if he has a problem with his ears....there are no parisites here and his ears are not infected....anyways...he has become extremely and violently posessive of his bed..or any place he sleeps. If anyone touches him while he is asleep he will lash out and bite. Also he has violent nightmares and bites the air. it's very strange. I'm afraid he has brain damage from the seizures. He is not nuetered...yet. anyone ever have this problem.