well out of all mine Zinniea's the only one I've ever had to syringe feed in over 2yrs (touch wood!) - although Primrose her sister seemed to be ill just after I'd got Zinniea better at Christmas, just a chase around the shed sorted her tummy ache out. So with it being the same rabbit all the time I'm more inclined to think it's the way she eats or something's frightened her - might be different with yours unless they're related, in which case it could be a genetic abnormality?