Aww I'm sorry for your loss

! As
@CCsGarden mentioned, my flock sadly did get poisoned last summer. It sounds similar to some of the behaviors you noticed. When I went out for my morning routine my chicken's water dish was fuller than I had left it and the water was cloudy. It had no odor. After noticing my rooster prohibiting all access to water I promptly emptied/cleaned all food and water dishes then dosed the entire flock why charcoal. Clearly, whatever was in the dish he'd already consumed a bit and it must've been an upper drug of sorts ( I already suspect my neighbors to not be up to the best things). My rooster exhibited many symptoms such as, dilated pupils, increased heart rate, overheating, acting "out of it" etc. I stayed with him all day constantly dunking him in an ice water bath because he was just sitting there about to heat stroke. After 24 hours he came off the "high" but never seemed quite normal. 4 months later I decided to put him down due to the fact that he lost all of his feathers and went from 14lbs to 7lbs

. It was a learning experience for sure but it reminded me of why I keep a rooster- to protect the hens. I narrowed it down to that day being too taxxing on his body and slowly causing organ failure. IF that's what happened with your chickens I'd suspect he drank too much or it was too concentrated and the effects happened quicker. I'm not trying to draw conclusions (I hope your neighbors would never do that

) but I'm happy to lend any knowledge I have from the experience! I sincerely wish your hen gets better, best wishes