Just 10 minutes ago I was out in the chicken yard and one of my 2 yr. old RIR hens starts sneezing repeatedly. It isn't just a normal sneeze but it is wracking her whole body and is sneezing clear fluid up to 2 ft. Then she goes into convulsions. I pick her up and try to check her out but the convulsions are so bad I couldn't even hold her. I took her out of the pen and she dies!!! She has shown NO symtoms of anything and has been eating well and pooping normal. Everything has been fine. There has been no change in food. NOTHING is different. She's been laying regularly. I mean NOTHING is different. Any ideas?