I'm sorry about your chicken.
I have a RIR that has been strange since Feb. I did make a post on here about her. She is a bantam. She has been acting strangely now for a few days since she started laying again. I don't know if it's coincidence or what? She went broody a few months back and then was happy and normal again since hatching out two chicks. (not her eggs). She had been active and fun for weeks. Now she laid a couple very large eggs and is acting all weird again. Sleepy, eyes closed, standing around hiding. Still eating. Very quiet.