A few weeks ago I found a dead healthy hen. There was no reason for her death so I was looking for some abnormal behaviors in the chickens. I have found nothing really strange. Normal behaviors, fine droppings, no sign of bugs. I just assumed the chicken died of old age or something but they are only 2 years old. I kind of forgot about the death until this morning. I let the chickens out and threw some mealworms, counted the chickens and noticed one was missing. I found myself inside to coop to fine one white leghorn hen sitting in a next box. Her head was arched and the feathers at the top of the arch were spiking up. Her comb was flopped over so I lifted it to see if she was asleep or something. But her eyes were wide open. Her pupils were small and she looked dead. I jumped and closed the door out of fear. I calmed down and opened it again. She kinda twitched and moved her head a little bit but stayed in place. I figured she was just lazy to rise so I left and came back to check on her 10 minutes later. When I walked in she was in the same place, with the comb flopped over her eye. I lifted it, to find her eyes closed and her body stiff. She didn't move and I came to the conclusion she had passed. She was another one of my healtiest. Do you have any idea what may be the problem? I'm honestly scared I'm gonna loose my whole flock including my chicks that are in the coop next door.