Hmmm... that is odd. There are a few things that come to mind: One, these could be "petit mal" seizures, two, they could be evidence of hyperthryoidism, or three, they could be due to an electrolyte imbalance (such as low potassium, which can happen with kidney problems) .
1. With seizure disorders, animals can either have "grand mal" seizures where the whole body is involved, or they can have petit- mal seizures where just the head is involved. Regardless of which type they have, seizures usually last a few seconds to a few minutes. There is often a very brief phase before-hand (seconds to minutes) where they seem disoriented, and a longer phase afterward (5 to 60 minutes) where they seem disoriented. In a cat Nena's age, seizures could be brought on by an inflammation in the brain, by epilepsy, by low blood sugar or by a tumor in the brain.
Here is more information http://www.petplace.com/cats/seizure-disorders-in-cats/page1.aspx
2. With hyperthryroidism, the thyroid gland produces too much of a hormone called T4 that controls metabolic rate. Being hyperthryroid is like being me on 8 cups of coffee - jittery, restless, very active. Usually there is weight loss. However, if Nena were in the very early stages, she could just have small "thryoid storms" with muscle fasciculations.
More information is here: http://www.petplace.com/cats/hyperthyroidism/page1.aspx
3. It's possible that Nena has low potassium levels which can happen with kidney disorders. Again, they usually show weight loss before they get to a point where they would have low potassium, but every cat is different.
Here is more information: http://www.petplace.com/cats/chronic-renal-kidney-failure-in-cats/page1.aspx
So, there are a number of possibilities for what might be going on. If Nena came in to see me, I would do a complete physical exam incuding a neurological exam. I would also recommend blood and urine analysis to check her thryoid and kidney function.
One thing which would be tremendously helpful to your vet would be if you could videotape the episode (on a cell phone perhaps as that might be closeby). Does it look anything like this?
This video always disturbs me because THIS is what a cat looks like when it seizures.
BotXXXXX XXXXXne, Nena does need to be seen by her vet to get to the bottom of this. If this has been helpful, please hit the green "Accept" button. I will still be here to provide more information if you need it.
And I LOVE to get updates down the road on how pets I "meet" on here are doing!