Hi! I know this is an old thread and people might not be responding anymore. When my Cayugas were between 2-5 weeks old, I had one duckling that had this same issue happen and I was sure it was a seizure - even though others told me the duck was just startled. Well, now that duckling is 3.5 months old and veryyyy odd compared to any of the other ducks I have had. She is very sweet, but she basically panics over any minor change in her environment. She will also quack her head off for me to come outside - I will and she will quiet down and be happy, but then if I get within 3 feet of her she acts like i'm going to beat her or something! None of my others are like this. There are also differences in the way she walks.
I wondered if you had noticed any of these differences in your duck(s) that had seizures. I am feeling like she may have neurological damage or something.