Hen dropped over this morning

[Chestoah]

This morning when my daughter let the hens out to forage, one of my hens walked out and just fell over. She layed on her back for a minute or two breathing heavily with eyes closed, spasmed a few times and died. Do you think this was a heart attack or an illness? Should I be worried about my other hens? Please help

 

[ChickenCanoe]

No way to tell without lab work. If you want to know for sure, send the bird to your state poultry lab for necropsy.

https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf