Our nearly 4 month old light brahma just died. She'd been acting sluggish. Standing in one spot for hours, eyes closed, wings down, head tucked in. I've seen her poop (normal), vent was clear. She would eat and drink but not as much as usual. I brought her inside to observe/examine her better. Don't know if it put her over the edge but with in 15 minutes she could no longer stand, her head was listing, she started a panting/retching type movement that turned in to loud bawks, then she sort of seizured for a minute and died. I was filming her behavior/symptoms and unwittingly filmed her dying. It happened so fast. She had acted like this for a few days. She was even acting like this 3 weeks ago but perked back up. They are on medicated feed and we use DE. I'm not sure if there is some preventative measures I should take for the rest of the chickens (there are 5 others) all of them seem perfectly normal.