First of all, congrats on having a 3 year old! How rare that is to hear from people in the rat community. That sounds pretty much like a seizure to me, akin to the way I've heard of it happening in people. The aftermath of a seizure can vary, I think. I have known a couple of people with epilepsy, and it affected both people very differently. One person I knew had it as a child and outgrew it, describing it as something that caused her embarrassment as a child but didn't really cause pain. The other is severely developmentally delayed because of brain damage sustained during each seizure - but this is so so so so so rare. (I believe it was mentioned to me that only a few people in the world have this particular type of seizure activity).
Of course, I'm no seizure expert. There are a few things that can cause seizures besides just having a solid diagnosis of epilepsy. As it goes, I can only really say what can cause it in humans, but it can't be too different for rats. People with heat stroke can have seizures, as can people with blood sugar problems. I've also read that hormonal causes and stress can contribute to seizures in some people. Electric shock, poisoning, allergic reactions, fevers, meningitis - all of these things can cause seizures as well. Brain tumors are also notorious for causing this. I'm also pretty sure that strokes predispose you to having epilepsy. It could also be something unexplained, perhaps to do with age or just some genetic predisposition for "faulty wiring" in the head at an older age.
It is also possible that your ratty could have gotten into some forbidden foods or household chemicals, causing neurological damage. Poppy seeds and licorice have killed rats with their neurotoxic properties, and often cause seizures. Make sure that you check your pantry, nearby chemical cabinets, etc. for signs of being pillaged by rats. Any room that your rats have regular access to or even could have access to needs to be checked if there's a chance there might be some chemicals stored in there. If your rat got into something that he wasn't supposed to, this is also a possible cause. It may seem a little extreme, but violent episodes can be pretty serious and it's a good idea to make sure that this hasn't happened. Even if they got into a bag of salt or decided to eat a fair amount of dish soap, it could very well be too much for their little bodies to handle.
Make sure your love on him lots and watch his behavior. Definitely bring him to the vet as soon as you can, and if he has another seizure bring him in right away. If he'll stand for it, you may even just wrap him in a towel and hold him close to you as to ensure he doesn't hurt himself at the vet. (Though, I would suggest bringing a carrier in case the risk of other animal patients taking too much interest in your little guy is too high. Or if he tends to escape and wander off a lot). And, when he's having a seizure, follow the basic rules for handling seizures:
1. Don't put anything in his mouth. None of that wooden spoon stuff from the movies.
2. Don't attempt to feed or hydrate him during the seizure. I know it seems crazy, but some people really do think that giving someone water during a seizure will help somehow. I saw someone attempt to give an unconscious girl water and forced it into her mouth - NOT A GOOD IDEA. It's the same basic premise. They're not conscious enough to swallow safely and could aspirate it.
3. Unless he's in an unsafe place, don't move him. If you must, gently move him somewhere (with a firm enough grip to hold him while he's wriggling, but not too tight) that you guys can wait out the rest of the seizure without him hurting himself. Preferably, find a flat space on the ground, perhaps on top of a soft carpet or towel in case he thrashes his head around hard enough to harm himself.
4. Give him lots of love after the seizure. Pet him with caution, even during the seizure. A rat with a seizure and coming out of one will be disoriented and scared. Some rats can bite and scratch out of fear during this time. However, it's good to give him lots of love and attention throughout to ensure that he is as comfortable as possible. Stroke him to the best of his liking.
5. Get to the vet as soon as you can after it has happened.
