experienced rat owners: any thoughts on these neurological symptoms?

[Sandinista]

I've tried to make this as brief as possible. In short, I am seeing similar neurological symptoms in Juliet (a rat I had to put down last September due to these symptoms) and Bella (a young, spayed rat I have now). They don't seem typical of anything, so I'm hoping to draw on someone's experience.

Juliet at first seemed sluggish for a bit, but the vet could find nothing wrong. One night, she was being held and suddenly jumped to the floor, raced around in circles, panicking and then hid in a corner. After that, she began experiencing panic attacks coupled with seizures. She was initially diagnosed with hepatic encephalopathy and treated accordingly. However, her condition worsened. She would tear around her cage in terror and/or have violent seizures that flung her around and then be panicked and confused. Toward the end, she seemed to hate her cage and hate being returned to it. She eventually also developed a head tilt and coordination problems. All manner of antibiotics, NSAIDs and steroids were tried to no apparent effect and she was eventually put down in September. We didn't do a necropsy, but the vet and I were both leaning toward pituitary tumor. Juliet was about 1.5 years old when she was put down.

I have since moved and adopted four new rats, two sets of sisters. Bella, the rat I am currently concerned about, is about 9.5 months old and was spayed at about 5 months. For a long time, she has had little spasms/jerks in her sleep. They never seemed to bother or even really wake her and I'm not even sure if they're relevant now but I mention them just in case. A few weeks ago, she was asleep in her box when I heard a commotion from inside. She then ran out, seeming panicked and ran to the bottom of her cage. I picked her up and held her for a while. She seemed extremely spooked (would flinch when I raised my hand to pet her), but calmed down and returned to normal after a few minutes. I couldn't figure out what caused that.
Last night, she was sitting next to her cagemate when she began acting weird. All I could see was a flurry of frantic activity (though she remained in one place) and her tail going stiff. I tried to pick her up afterwards, but she panicked, shrieked and jumped out of my hands. I let her stay on the floor for a little while and watched her. Mostly, she just acted very scared; she's a bit skittish generally, but this was definitely to a different degree, as if something had REALLY frightened her. At one point, she got up on her hind paws and started batting her front paws in front of her face very quickly, which I've since read is associated with seizure activity. Shortly after that, I was able to pick her up and hold her until she calmed down. When I put her back in the cage, she acted normal, if slightly tired. In neither case can I think of any external stimulus (i.e. a loud noise) that triggered this.

These are pretty clearly neurological symptoms of something, but from everything I've read/observed, they are not typical for a pituitary tumor. Furthermore, it seems that Juliet developed her condition quite young (18 months), but Bella is even younger AND spayed. (I realize that a spay isn't a guarantee, but this just seems like a rather huge, unlikely coincidence.) The two rats are quite different--Juliet was endlessly outgoing, curious and energetic, whereas Bella is more shy, calm, reserved and lazy--and don't share many environmental factors (though they are on the same bedding and food and on filtered tap water, though probably not from the same source). And neither Juliet's cagemates nor Bella's seemed/seem to be at all affected.

The more I think about it, the more I wonder if it could be a problem with the tap water. Juliet and her cagemates were on filtered tap water. Bella and her cagemates were on bottled water from the beginning, but I recently switched to filtered tap (we were trying not to buy bottled in order to be environmentally conscious).

Any thoughts about what else might cause this would be so very appreciated.